1 Enzymes

1 Enzymes

1.1 Diagnostic enzymology

1.1.1 Enzymes in serum

1.1.1.1 Determination of enzyme activity

1.1.1.2 Isoenzymes and isoforms

1.1.1.3 Macroenzymes

1.1.1.4 Antibodies to tissue-specific enzymes

1.1.2 Diagnostic information of enzymes

1.1.3 Enzymes in the differential diagnosis of acute diseases

1.1.3.1 Differential diagnosis in acute thoracic and abdominal pain

1.1.3.2 Enzyme patterns in liver disease

1.1.3.3 Enzyme activities in intensive care patients

1.1.3.4 Enzyme activities in surgical interventions

1.1.3.5 Enzymes in cerebral seizures

1.1.3.6 Enzymes in cancer

1.1.4 Biological influence factors and interference factors

1.1.4.1 Biological influence factors

1.1.4.2 Interference factors

1.2 Biomarkers of liver disease

1.2.1 General clinical liver-associated tests

1.2.2 Determination of extrahepatic factors

1.3 Alkaline phosphatase (ALP)

1.3.1 Indication

1.3.2 Method of determination

1.3.2.1 Total ALP (orthophosphoric acid monoester phosphohydrolase, EC 3.1.3.1)

1.3.2.2 ALP isoenzymes and isoforms

1.3.3 Specimen

1.3.4 Reference interval

1.3.5 Clinical significance

1.3.5.1 Elevated activity of total ALP

1.3.5.2 Reduced ALP activity

1.3.6 Comments and problems

1.3.7 Pathophysiology

1.3.7.1 Liver ALP

1.3.7.2 Bone ALP

1.3.7.3 Intestinal ALP

1.3.7.4 Placental ALP

1.4 α-Amylase

1.4.1 Indication

1.4.2 Method of determination

1.4.3 Specimen

1.4.4 Reference interval

1.4.5 Clinical significance

1.4.5.1 α-Amylase in serum

1.4.5.2 α-Amylase in urine

1.4.5.3 α-Amylase in extravascular fluids

1.4.6 Comments and problems

1.4.7 Pathophysiology

1.5 Angiotensin-converting enzyme (ACE)

1.5.1 Indication

1.5.2 Method of determination

1.5.3 Specimen

1.5.4 Reference interval

1.5.5 Clinical significance

1.5.5.1 Sarcoidosis

1.5.5.2 Elevated SACE in other diseases

1.5.6 Comments and problems

1.5.7 Pathophysiology

1.6 Alanine aminotransferase (ALT), Aspartate aminotransferase (AST)

1.6.1 Indication

1.6.2 Method of determination

1.6.3 Specimen

1.6.4 Reference interval

1.6.5 Clinical significance

1.6.5.1 Liver diseases

1.6.5.1.1 Screening for liver disease

1.6.5.1.2 Medical decision-making approach in symptomatic patients

1.6.5.1.3 Severity assessment of liver disease

1.6.5.1.4 Liver disease staging

1.6.5.1.5 Etiological verification of liver disease

1.6.5.1.6 Prognostic assessment of hepatitis

1.6.5.2 Myopathies

1.6.6 Comments and problems

1.6.7 Pathophysiology

1.7 Cholinesterases (ChE)

1.7.1 Indication

1.7.2 Method of determination

1.7.2.1 Phenotyping of genetic variants

1.7.3 Specimen

1.7.4 Reference interval

1.7.5 Clinical significance

1.7.5.1 ChE in liver disease

1.7.5.2 Drug-induced ChE inhibition

1.7.5.3 ChE in pesticide poisoning

1.7.5.4 ChE reduction by atypical variants

1.7.5.5 Elevated ChE activity

1.7.6 Comments and problems

1.7.7 Pathophysiology

1.8 Creatine kinase (CK)

1.8.1 Indication

1.8.2 Method of determination

1.8.3 Specimen

1.8.4 Reference interval

1.8.5 Clinical significance

1.8.6 Comments and problems

1.8.7 Pathophysiology

1.9 Gamma-glutamyl transferase (GGT)

1.9.1 Indication

1.9.2 Method of determination

1.9.3 Specimen

1.9.4 Reference interval

1.9.5 Clinical significance

1.9.5.1 Elevated GGT

1.9.5.2 Diagnostic sensitivity and specificity of GGT for liver diseases

1.9.5.3 Isolated elevation of GGT

1.9.5.4 Differential diagnostic significance of GGT

1.9.5.5 Differentiation of cholestasis from inflammatory liver diseases

1.9.5.6 GGT as biomarker of alcoholism

1.9.6 Comments and problems

1.9.7 Pathophysiology

1.10 Glutamate dehydrogenase (GLD)

1.10.1 Indication

1.10.2 Method of determination

1.10.3 Specimen

1.10.4 Reference interval

1.10.5 Clinical significance

1.10.5.1 Differential diagnosis of jaundice

1.10.5.2 Differential diagnosis of severe liver injury

1.10.5.3 Indicator of alcohol addiction

1.10.6 Comments and problems

1.10.7 Pathophysiology

1.11 Lactate dehydrogenase (LD)

1.11.1 Indication

1.11.2 Method of determination

1.11.3 Specimen

1.11.4 Reference interval

1.11.5 Clinical significance

1.11.6 Comments and problems

1.11.7 Pathophysiology

1.12 Lipase

1.12.1 Indication

1.12.2 Method of determination

1.12.3 Specimen

1.12.4 Reference interval

1.12.5 Clinical significance

1.12.6 Comments and problems

1.12.7 Pathophysiology

1.13 Acid phosphatase (ACP)

1.13.1 Indication

1.13.2 Method of determination

1.13.3 Specimen

1.13.4 Reference interval

1.13.5 Clinical significance

Laboratory investigations

1.1 Enzyme diagnostics

1.1.1.3 Macroenzymes

1.1.3 Enzymes in the differentiation of acute diseases

1.2 Biomarkers of liver disease

1.3 Alkaline phosphatase (ALP)

1.4 α-Amylase

1.5 Angiotensin Converting Enzyme (ACE)

1.6 Alanin-Aminotransferase (ALT), Aspartat-Aminotransferase (AST)

1.7 Cholinesterase (ChE)

1.8 Creatinkinase (CK)

1.9 Gamma Glutamyl Transferase (GGT)

1.10 Glutamat Dehydrogenase (GLD)

1.11 Lactat Dehydrogenase (LD)

1.12 Lipase

1.13 Acid phosphatase (ACP)

Diseases associated with the elevation of enzymes

α1-Antitrypsin deficiency

– AIDS therapy: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Acute liver infections due to non-hepatotropic viruses

– Brucellosis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Leptospirosis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Q-fever: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Toxoplasmosis: Table 1.6-3: Aminotransferases in patients with hepatopathies

Acute pancreatitis

– Table 1.12-3: Causes of elevated lipase in serum

– Table 1.9-5: Various causes of elevated GGT levels

– Table 1.4-2: Causes of pancreatogenous hyperamylasemia

Acute viral hepatitis due to hepatotropic viruses

– Hepatitis A: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Hepatitis B: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Hepatitis C: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Hepatitis D: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Hepatitis E: Table 1.6-3: Aminotransferases in patients with hepatopathies

Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.9-4: GGT in hepatic and biliary tract diseases

– Table 1.10-4: GLD in hepatic and biliary tract diseases

Alcoholic hepatopathy

– Alcoholic fatty liver: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Alcoholic hepatitis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Alcoholic hepatitis: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Amylase: Table 1.4-3: Causes of extrapancreatic hyperamylasemias

– Fatty liver: Table 1.6-3: Aminotransferases in patients with hepatopathies

– GGT: Table 1.9-4: GGT in hepatic and biliary tract diseases

– GLD: Table 1.10-4: GLD in hepatic and biliary tract diseases

Acromegaly

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Acute abdomen

– Table 1.4-2: Causes of pancreatogenous hyperamylasemia

– Table 1.8-7: CK activity in other tissue damage

– Table 1.12-3: Causes of elevated lipase in serum

Acute circulatory disorder

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

– Table 1.9-4: GGT in hepatic and biliary tract diseases

Acute Hepatitis

– ALP: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

– CHE: Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

– CK: Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

Amiodarone

Table 1.6-3: Aminotransferases in patients with hepatopathies

Anorexia nervosa

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Autoimmune liver disease

– Table 1.2-5: Biomarkers in hepatopathies

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Autoimmune hepatitis (AIH): Table 1.6-3: Aminotransferases in patients with hepatopathies

– Primary sclerosing cholangitis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Primary biliary cirrhosis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Aspartate aminotransferase-to-platelet ratio index (APRI): Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

Autologous stem cell transplantation

– Table 1.11-4: Diseases that may cause elevated LD in serum

BARD Score

– Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

Bone disease

– Osteomalacia: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Osteoporosis: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Osteosarcoma, Ewing sarcoma: Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

– Primary hyperparathyroidism: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Corticosteroid induced osteoporosis: Table 1.3-7: Diseases associated with low ALP levels

Brain tumor, cerebral hemorrohage

– Table 1.9-5: Various causes of elevated GGT levels

Cardiac disease

– Angina pectoris: Table 1.8-4: CK and CK-MB activities in acute myocardial injury

– Coronary heart disease: Table 1.7-9: Diseases possibly associated with elevated ChE activity

– Coronary event: Table 1.9-5: Various causes of elevated GGT levels

– Myocardial infarction: Table 1.8-4: CK and CK-MB activities in acute myocardial injury

– Myocardial infarction: Table 1.9-5: Various causes of elevated GGT levels

– Myocardial infarction: pernicious anemia, trichinosis: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Cardiac catheterization: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Heart rhythm disturbances: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Myocarditis: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Myocarditis: Table 1.8-4: CK and CK-MB activities in acute myocardial injury

– Pace maker implantation: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms: Table 1.11-4: Diseases that may cause elevated LD in serum

– Various: Table 1.11-4: Diseases that may cause elevated LD in serum

Cholestasis

– Biliary atresia: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Bylers syndrome: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Extrahepatic cholestasis: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Intrahepatic cholestasis: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Intrahepatic cholestasis of pregnancy, ICP: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Primary sclerosing cholangitis (PSC):Table 1.9-4: GGT in hepatic and biliary tract diseases

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

– Table 1.9-4: GGT in hepatic and biliary tract diseases

Cholestatic syndrome

– Acute hepatitis, cholestatic course: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Bacterial infection: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Extrahepatic obstructive jaundice: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Intrahepatic cholestasis: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

– Idiopathic post-operative cholestassis: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Obstructive jaundice: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

– Obstructive jaundice: Table 1.10-4: GLD in hepatic and biliary tract diseases

Chronically ill

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Chronic berylliosis

– Table 1.7-6: Other diseases possibly associated with reduced ChE activity

Chronic fatique syndrome

– Table 1.2-5: Biomarkers in hepatopathies

Chronic intestinal disease

– Table 1.7-6: Other diseases possibly associated with reduced ChE activity

Chronic muscle damage

– Chronic myositis: Table 1.8-6: CK activity in chronic skeletal muscle damage

– Muscle dystrophia: Table 1.8-6: CK activity in chronic skeletal muscle damage

– Primary myopathy: Table 1.8-6: CK activity in chronic skeletal muscle damage

Chronic pancreatitis

– Table 1.12-3: Causes of elevated lipase in serum

– Table 1.4-2: Causes of pancreatogenous hyperamylasemia

Chronic viral hepatitis

– Chronic hepatitis B Infection: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Chronic hepatitis C Infection: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

– Table 1.9-4: GGT in hepatic and biliary tract diseases

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

– Table 1.10-4: GLD in hepatic and biliary tract diseases

Competitive sport

– Table 1.11-4: Diseases that may cause elevated LD in serum

Crohn’s disease

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease, Morbus Gaucher, Morbus Niemann-Pick

– Table 1.13-2: Diseases possibly associated with elevated ACP in serum

Cynthiana-variant

– Table 1.7-9: Diseases possibly associated with elevated ChE activity

Diabetes mellitus

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease

– Table 1.5-2: Elevated ACE at other diseases and conditions

– Table 1.7-9: Diseases possibly associated with elevated ChE activity

Drug related heptotoxicity

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

– Table 1.9-4: GGT in hepatic and biliary tract diseases

– Table 1.10-4: GLD in hepatic and biliary tract diseases

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Antiepileptics: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Antihypertensives: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Cyclophosphamide, Busulfan, Azathioprine: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Heparin: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Lipid-lowering agents: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Methotrexate: Table 1.6-3: Aminotransferases in patients with hepatopathies

– NSAID: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Oral antidiabetics: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Oral ovulation inhibitor, Danazol: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Paracetamol, INH, Troglitazone, Halothan, Sulfonamide: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Psychotropic medication: Table 1.6-3: Aminotransferases in patients with hepatopathies

Ecstasy

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Enteritis regionalis, ulcerous colitis

– Table 1.12-3: Causes of elevated lipase in serum

ERCP

– Table 1.4-2: Causes of pancreatogenous hyperamylasemia

– Table 1.12-3: Causes of elevated lipase in serum

G-CSF therapy

– Table 1.11-4: Diseases that may cause elevated LD in serum

– Lung cancer: Table 1.11-4: Diseases that may cause elevated LD in serum

Growth hormone treatment

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Hard physical work

– Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

Heat stroke

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Hematologic disease

– Hemolytic anemia: Table 1.11-4: Diseases that may cause elevated LD in serum

Essential thrombocythemia: Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.8-7: CK activity in other tissue damage

Hepatitis A

– Table 1.2-5: Biomarkers in hepatopathies

Hepatitis B

– Chronic HBV infection: Table 1.2-5: Biomarkers in hepatopathies

– Liver cirrhosis: Table 1.2-5: Biomarkers in hepatopathies

Hepatitis C

– Chronic HCV infection: Table 1.2-5: Biomarkers in hepatopathies

Hepatitis D

– Table 1.2-5: Biomarkers in hepatopathies

Hepatitis E

– Table 1.2-5: Biomarkers in hepatopathies

Hepatitis due to non-hepatotropic viruses

– Adenovirus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Cytomegaly virus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Enterovirus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Epstein-Barr virus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Herpes-simplex virus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Rubella virus: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Varicella-zoster virus: Table 1.6-3: Aminotransferases in patients with hepatopathies

Hepatitis due to other pathogens

– Table 1.2-5: Biomarkers in hepatopathies

Hepatopathy

– Table 1.4-3: Causes of extra pancreatic hyperamylasemias

Hepatopathy in pregnancy

– HELLP syndrome: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Hyperemesis gravidarum: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Intrahepatic cholestasis of pregnancy: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Preeclampsiea, eclampsia: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Fatty liver of pregnancy: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Enhanced Liver Fibrosis (ELF) score: Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

Herbal medicines

– Table 1.6-3: Aminotransferases in patients with hepatopathies

HIV infection

– Table 1.5-2: Elevated ACE at other diseases and conditions

Hodgkin lymphoma, non-Hodgkin lymphoma

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP)

Hyperlipoproteinemia type IV

– Table 1.7-9: Diseases possibly associated with elevated ChE activity

Hyperparathyroidism, multiple myeloma, osteosarcoma, osteogenesis imperfecta, renal osteodystrophy

– Table 1.13-2: Diseases possibly associated with elevated ACP in serum

Hyperthyroidism

– Adiposity: Table 1.7-9: Diseases possibly associated with elevated ChE activity

– Myopathy: Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease

Hypoxic hepatopathy

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.10-4: GLD in hepatic and biliary tract diseases.Idiopathic pulmonary fibrosis

– Table 1.11-4: Diseases that may cause elevated LD in serum

Icterus juvenilis intermittens Gilbert-Meulengracht

– Table 1.7-9: Diseases possibly associated with elevated ChE activity

Incapacity of work

– Table 1.9-5: Various causes of elevated GGT levels

Intramuscular injection

– Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

Korean hemorrhagic fever

– Table 1.11-4: Diseases that may cause elevated LD in serum

Leukemia, polycythemia, thrombocythemia, megaloblastic anemia: Table 1.13-2: Diseases possibly associated with elevated ACP in serum

– Liver tumors other than hepatocellular carcinoma: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Table 1.11-4: Diseases that may cause elevated LD in serum

Liver abscess

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

Liver cell carcinoma

– Metastatic liver disease: Table 1.10-4: GLD in hepatic and biliary tract diseases

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Liver cirrhosis

– Primary biliary cirrhosis: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Table 1.9-4: GGT in hepatic and biliary tract diseases

– Table 1.10-4: GLD in hepatic and biliary tract diseases

Liver disease

– Acute liver failure: Table 1.6-3: Aminotransferases in patients with hepatopathies

– Acute toxic liver disease: Table 1.10-4: GLD in hepatic and biliary tract diseases

– Amyloidosis of the liver: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Portals hypertension: Table 1.11-4: Diseases that may cause elevated LD in serum

– Fatty liver: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Fatty liver: Table 1.7-9: Diseases possibly associated with elevated ChE activity

– Fatty liver: Table 1.9-4: GGT in hepatic and biliary tract diseases

– Forns Score: Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

– Guci-index: Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

– Infectious mononucleosis: Table 1.11-4: Diseases that may cause elevated LD in serum

– Primary sclerosing cholangitis: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Tissue damage: Table 1.8-7: CK activity in other tissue damage

– Tumors of the liver: Table 1.11-4: Diseases that may cause elevated LD in serum

Liver metastasis

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

Liver transplant

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

– Monitoring after liver transplantation: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

Liver tumors other than hepatocellular carcinoma

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.7-4: Liver diseases possibly associated with decreased ChE activity

Long-term survival

– Table 1.9-5: Various causes of elevated GGT levels

Lung disease

– Pulmonary embolism: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Pulmonary embolism: Table 1.11-4: Diseases that may cause elevated LD in serum

Table 1.11-4: Diseases that may cause elevated LD in serum

Macroamylasemia

– Table 1.4-3: Causes of extra pancreatic hyperamylasemias

Malignant hyperthermia

– Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

Malignant tumor

– Dysgerminoma: Table 1.11-4: Diseases that may cause elevated LD in serum

– Breast carcinoma: Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

– Leukemia: Table 1.11-4: Diseases that may cause elevated LD in serum

– Hodgkin’s disease: Table 1.11-4: Diseases that may cause elevated LD in serum

– Multiple myeloma: Table 1.11-4: Diseases that may cause elevated LD in serum

– Neuroblastoma: Table 1.11-4: Diseases that may cause elevated LD in serum

– Non-Hodgkin lymphoma: Table 1.11-4: Diseases that may cause elevated LD in serum

– Primary liver cell carcinoma: Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

– Prostate carcinoma: Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

– Prostate carcinoma: Table 1.13-2: Diseases possibly associated with elevated ACP in serum

– Testicular tumor: Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

– Testicular tumor: Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.4-3: Causes of extra pancreatic hyperamylasemias

– Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.12-3: Causes of elevated lipase in serum

– Table 1.13-2: Diseases possibly associated with elevated ACP in serum

Megaloblastic anemia

– Table 1.11-4: Diseases that may cause elevated LD in serum

Metabolic syndrome

– Table 1.9-5: Various causes of elevated GGT levels

Mixed connective tissue disease

– Table 1.5-2: Elevated ACE at other diseases and conditions

Morbus Gaucher

– Table 1.5-2: Elevated ACE at other diseases and conditions

Multiple myeloma

– Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

Muscle disease

– Myositis: Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

– Progressive musclular dystrophy: Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

– Rhabdomyolysis: Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

– Secondary myopathy: Table 1.8-6: CK activity in chronic skeletal muscle damage

– Table 1.7-6: Other diseases possibly associated with reduced ChE activity

– Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

NAFLD und NASH

– NAFLD fibrosis Score: Table 1.2-1: Hepatic fibrosis staging based on scores and serum markers

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Neurologic disease

– Table 1.8-7: CK activity in other tissue damage

Paget’s disease

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Paraneoplastic syndrome

– Table 1.3-5: ALP as biomarker in malignant tumors and bone metastases

Parenteral nutrition

Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.9-4: GGT in hepatic and biliary tract diseases

Parotitis

– Table 1.4-3: Causes of extra pancreatic hyperamylasemias

Pericarditis

– Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

Phenprocoumon-induced hepatitis

– Table 1.3-3: Hepatic and biliary tract diseases possibly associated with elevated total ALP

Pneumonia (Pneumocystis carinii)

– Table 1.11-4: Diseases that may cause elevated LD in serum

Poisoning

– Table 1.9-4: GGT in hepatic and biliary tract diseases

Renal disease

– Nephrotic syndrome, exudative enteropathy: Table 1.7-9: Diseases possibly associated with elevated ChE activity

– Renal infarction: Table 1.11-4: Diseases that may cause elevated LD in serum

– Renal insufficiency: Table 1.4-3: Causes of extra pancreatic hyperamylasemias

– Renal insufficiency: Table 1.12-3: Causes of elevated lipase in serum

– Renal transplantation: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Table 1.9-5: Various causes of elevated GGT levels

Renal tubular disease

– de Toni-Debré Fanconi syndrome: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Phosphate diabetes: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Phosphate diabetes and neurofibromatosis: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Renal tubular acidosis: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Renal osteodystrophy: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– X-linked phosphate diabetes: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Rheumatic disease

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease

– Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Shock

– Intensive care patient: Table 1.7-6: Other diseases possibly associated with reduced ChE activity

– Pregnancy: Table 1.11-4: Diseases that may cause elevated LD in serum

– Serious illness: Table 1.8-7: CK activity in other tissue damage

– Septic Shock: Table 1.7-6: Other diseases possibly associated with reduced ChE activity

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease

– Table 1.5-2: Elevated ACE at other diseases and conditions

– Table 1.8-7: CK activity in other tissue damage

Skeletal muscle disease

– Dermatomyositis, polymyositis: Table 1.11-4: Diseases that may cause elevated LD in serum

– Neurogenic muscle atrophy: Table 1.11-4: Diseases that may cause elevated LD in serum

– Progressive muscle atrophy: Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.11-4: Diseases that may cause elevated LD in serum

Smoking and alcohol

– Table 1.9-5: Various causes of elevated GGT levels

Statins

– Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

Status epilepticus

– Table 1.6-5: Aminotransferase behavior in skeletal muscle damage

– Table 1.11-4: Diseases that may cause elevated LD in serum

Surgical intervention

– Open heart surgery: Table 1.6-4: Aminotransferases in cardiac diseases and diseases with similar symptoms

– Postoperative: Table 1.11-4: Diseases that may cause elevated LD in serum

– Table 1.8-5: CK and CK-MB activities in acute skeletal muscle damage

Thrombotic thrombocytopenic purpura

– Table 1.11-4: Diseases that may cause elevated LD in serum

Transient hyperphosphatasemia

– Table 1.3-6: Elevated ALP without recognizable hepatobiliary disease or bone disease

Tumorlysis syndrome

– Table 1.11-4: Diseases that may cause elevated LD in serum

Vitamin D

– Antiepileptics, phenytoin, phenobarbital, primidone, carbamazepine: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Antihypertensives: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Deficiency: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

– Pseudo vitamin D deficiency: Table 1.3-4: Diseases of the skeletal system associated with elevated total ALP

Wilson disease

– Hypophosphatasia: Table 1.3-7: Diseases associated with low ALP levels

– Table 1.6-3: Aminotransferases in patients with hepatopathies

Xenobiotics

– Carbon tetrachloride, mushroom poison (phalloidin, phalloin): Table 1.6-3: Aminotransferases in patients with hepatopathies

– Table 1.9-4: GGT in hepatic and biliary tract diseases

1.1 Diagnostic enzymology

Lothar Thomas

1.1.1 Enzymes in serum

The enzymes measured in serum, plasma and extravascular fluids for diagnostic purposes are biocatalysts. Even minor quantities are sufficient to attain the equilibrium of a chemical reaction by lowering the activation energy. Enzymes have a reaction specificity meaning that a chemical reaction can only be catalyzed by an enzyme specifically required for this reaction. Furthermore, enzymes have a substrate specificity meaning that only a specific substance or substance group functions as a reactant and is converted to the product.

Factors influencing enzyme activity

The enzymes in serum come from tissue cells or result from secretory enzymes entering the blood. The tissue enzymes mainly originate from the cells” main metabolic chains. In the cells, they are either dissolved in the cytoplasm or bound to cell structures such as the mitochondria. Secretory enzymes such as peptidases and hydrolases are usually secreted in an inactive form, while only a few enzymes such as cholinesterases pass into the plasma in an active form. Enzyme activity in the plasma depends on factors governing the extent of release. The release of cell-specific enzymes is regulated by the extent of cell damage. Increased enzyme production of individual cells or the proliferation of enzyme-producing tissue are decisive for the release of secretory enzymes /1/.

Enzyme release: Low activity of cell-specific enzymes in the blood of healthy individuals is based on the impermeability of the metabolically active cell membrane. Any pathological process affecting the cell membrane’s energy supply, for example inadequate supply with ATP or other high-energy substrates due to ischemia or anoxia, can cause disintegration of the cell membrane and consecutive release of enzymes. First, the membrane potential is upset. K+ leaves the cell and Na+ and water enter the cell causing swelling. Subsequent Ca2+ entry activates hydrolases and peptidases which results in the destruction of intracellular structures and leakage of the cell membrane. Cytoplasmic enzymes are the first to appear in the blood, followed by mitochondrial and membrane-bound enzymes. The extent and rate of enzyme release depend on the size and the concentration gradient of a given enzyme between cytoplasm and extracellular space. In healthy individuals, intracellular enzyme concentration is very much higher than the concentration in plasma. For example, the AST and ALT activities in the liver, kidney, heart and skeletal muscle are higher than in the plasma of a healthy individual as follows:

Enzymes pass from the interstitium to the blood either via direct transfer across the capillary wall or indirectly via the lymphatic pathways. Direct transfer is the case in well-vascularized tissue such as the liver parenchyma, and indirect transfer takes places in tissue with a less permeable capillary membrane such as the muscles. The extent of enzyme release depends on the enzyme’s intracellular localization. Enzymes dissolved in cytoplasm appear in the blood relatively soon after cell damage with an easily measurable activity. Enzymes bound to subcellular structures such as the mitochondria take longer. As a rule, an enzyme pattern corresponding to the intracellular enzyme distribution appears in the blood within 24 hours after cell damage including necrosis /1/.

Changes in enzyme production: Changes in enzyme production can manifest as reduced or elevated activity in the blood compared to the reference interval without the presence of cell damage. Reduced activity is less in the focus of diagnostic attention as it is mainly based on genetic dysfunction of the tissue enzymes such as ALP. In contrast, reduced activity in secretory enzymes is often based on a reduction in the relevant enzyme-producing tissue, for example reduced CHE in liver cirrhosis. Increased enzyme release into the blood without the presence of tissue damage can have the following causes:

Tissue damage and enzyme elevation

The most common enzyme elevations are caused by damage of the liver, myocardium, skeletal muscle and erythrocytes. Liver-induced enzyme elevations result from direct damage of the cell membrane by viruses, the toxic effect of drugs and poisons or tissue hypoxia. The latter usually causes centrilobular necrosis of hepatocytes and can result from acute right heart failure, portal hypertension or arterial hypoxia, for example, in cases of shock. In contrast, hepatic infarctions are rare because the liver has a dual blood supply from the hepatic arteries and the portal vein system.

The situation is different for the heart. As a rule, occlusion of the end arteries results in hypoxemic necrosis of myocytes due to the segmental blood supply of the myocardium. An enzyme pattern corresponding to that of the myocardial cell appears in the blood within 24 hours.

Damage to the skeletal muscles associated with enzyme release is manifold, the most important being injuries, hypoxic necroses, inflammations, infections, degenerative diseases, toxic damage (alcohol), uremia and neurogenic myopathies.

The lysis of erythrocytes causes the release of LD, the enzyme with the highest activity in these cells. A distinction is made between in-vivo and in-vitro hemolysis. In-vivo hemolysis occurs within the blood vessel (intravascular) and is immune-mediated in most cases, while in-vitro hemolysis is based on the destruction of the erythrocytes during blood sampling or several days of storing of whole blood prior to analysis.

In kinetic techniques used in clinical chemical routine diagnostics to determine the enzyme activity, concentrations of up to 10–10 mol/L have been identified. This high analytical sensitivity allows the detection of even minor tissue damage by enzymatic analysis. Even if only 1 in approx. 750 hepatocytes is damaged, this induces elevated ALT levels to beyond the upper reference limit.

Clearance of serum enzymes

It is important to know about the clearance of enzymes in order to asses the enzyme activity as a diagnostic biomarker of organic diseases. Low-molecular enzymes such as the α-amylase are partly eliminated renally. Primarily, however, enzymes passing from the tissues into the blood are internalized in the cells of the reticuloendothelial system via receptor-mediated endocytosis.

There are, for example, specific receptors on the hepatocyte cell membrane that react with the N-galactosyl residues of the intestinal isoenzyme of ALP. This results in intracellular degradation into peptides available for participation in metabolic processes. The half-life of many enzymes in the blood is 4–24 hours (Tab. 1.1-1 – Half-lives of serum enzymes). It can be extended as a result of complexing of the enzyme with immunoglobulins or impaired function of the tissues or organs responsible for the clearance. In liver cirrhosis, for example, the clearance of enzymes is lowered due to a reduction in liver tissue. The half-life of α-amylase can be extended as a result of renal insufficiency or complexing with immunoglobulin as, for example, in cases of macroamylasemia.

1.1.1.1 Determination of enzymatic activity

The essential characteristic of an enzyme (E) is its ability to catalyze the conversion of a substance, also referred to as substrate (S), into a product (P). This happens according to the following reaction process /2/:

E+S → ES → E+P

In a first reaction step, the substrate binds to the enzyme forming the enzyme-substrate complex; the substrate part of this complex is converted to a product and the product is released. The released enzyme immediately binds another substrate molecule. The turnover number of most enzymes is at least 100 substrate molecules per enzyme molecule per second.

The determination of the conversion rate, measured as change of a substance (decrease in substrate or increase in product) per time unit, provides the basis for quantitative enzyme analysis. In enzyme analysis, the conversion rate is also referred to as reaction rate.

The concentration of an enzyme is determined by measuring the enzyme’s catalytic activity. The activity is preferably determined by kinetic assay.

Kinetic assay /2/: Under conditions where the concentration of the enzyme is much lower in the assay medium than that of its substrate, many enzymes behave according to the Michaelis-Menten model that correlates the velocity of an enzymatic reaction with the molar concentration of the enzyme and its substrate. Thus, the following correlation exists between the reaction velocity V of the enzyme reaction, its maximum velocity (Vmax) and the substrate concentration [S]:

V = V max · [S] K m + [S]

The Michaelis-Menten constant (Km) is the substrate concentration, at which half of Vmax of an enzyme-catalyzed reaction is reached. As a rule, it is 10–2 to 10–5 mol/L. The lower the value of Km, the higher is the affinity of the substrate to the enzyme. Under defined conditions such as temperature, pH value, ionic strength etc and at constant enzyme concentration, the correlation between V and [S] follows a hyperbola that approaches the maximum Vmax asymptotically. If [S] is much more abundant compared to Km, V is independent of [S]. In this case, we say that the enzyme is saturated with substrate. Here, the amount of substrate converted by the enzyme is proportional to the amount of enzyme in the assay medium and the duration of the reaction.

The Michaelis-Menten model is inadequate to describe enzymatic reactions where individual participants show cooperative behavior, enzymes with allosteric reactions and multi-substrate reactions.

Photometric measurement of enzyme reaction /3/: The photometric measurement of an enzyme reaction is based on a change in light absorption (∆A) during a time interval (∆t) due to the decrease in substrate concentration or increase in product concentration. The change in absorption (∆A/∆t) is converted to a change in substrate or product concentration over time. This is done by multiplication with the factor V/ε x l, where V is the volume of the assay medium, ε is the molar absorption coefficient and l is the length of the light path through the cuvette. ∆A is non-dimensional; the dimensions of the other variables are T = ∆t, L3 = volume V, L2 × N–1 = ε, N = substrate concentration and L= Liter. The reaction rate is calculated according to the following equation:

ΔA × V corresponding to 1 × L 3 = N × T –1 Δt ε × l T L 2 × N –1 × L

N × T–1 is the amount of substrate turned over per time unit or the amount of product yielded per time unit and indicates the catalytic activity of an enzyme. The catalytic activity is given in katal.

The photometric analysis of the amount of turned-over substrate or the resulting amount of product is based on the principle of light absorption by an absorbing substance in a non-absorbing solvent according to the Bouguer-Lambert-Beer law.

A = ε × c × d

A is the absorption, c the substrate or product concentration, d the length of the light path through the cuvette and ε the molar decadic absorption coefficient of the substrate or product measured. The dimension of ε follows from:

ε = A/c × d = 1 × mol–1 × mm–1

The physiological substrates and products of most enzymes are colorless. Therefore, synthetic (chromogenic) substrates are used where a colored reaction product is obtained or an indicator reaction is arranged after the actual measurement reaction. In some enzymes that react directly with the co-substrates (co-enzymes) NADH2 and NADPH2 resulting in the oxidized co-enzyme forms NAD or NADP, the decline in NADH2 and NADPH2 is determined at 344 nm, 334 nm or 365 nm as indicator of enzymatic activity (simple optical assay). The reaction for the determination of LD is a typical example of a simple optical assay (see Section 1.11 – Lactate dehydrogenase (LD)). If the substrate produced in the measurement reaction cannot be immediately determined by photometry, it is associated with the indicator reaction through an auxiliary reaction in a reaction sequence involving the co-enzymes NADP/NADPH2. The reaction for the determination of CK is an example of this (see Section 1.8 – Creatine kinase (CK)).

Comparable results can only be obtained if enzyme activities are measured at the same conditions. Therefore, the International Federation of Clinical Chemistry (IFCC) established a reference system for the measurement of the catalytic activity of many enzymes /4/. The measurement temperature is 37 °C. The reference system comprises primary reference methods, certified reference preparations and a worldwide network of reference laboratories.

The enzymatic activity is given in kinetic units because the enzymes are determined quantitatively based on their catalytic activity. The following units are defined:

1.1.1.2 Isoenzymes and isoforms

Isoenzymes

According to the IUPAC-IUB Commission on Biochemical Nomenclature, isoenzymes are defined as follows: Proteins with similar enzymatic activity encoded by different genes. Besides different amino acid sequence and different catalytic properties, they can differ in regards to affinity to substrates, activators and inhibitors, optimal pH and temperature and heat stability. The following categories of isoenzymes are distinguished /5/:

Isoforms

Enzyme isoforms result from post translational modification of an enzyme, for example the tissue-nonspecific ALP from which the isoforms of liver ALP, bone ALP and kidney ALP are formed post translationally.

Isoenzyme and isoform analysis

Determination of activity: An isoenzyme family can have similar, but not identical, catalytic activities. They mostly differ slightly in optimal pH, affinity constants for the substrate and sensitivity to inhibitors or denaturing reagents. Alloenzymes can, but do not necessarily have to, differ in their catalytic activity. Severe or even terminal illness can result if it is due to the mutant allele that an enzyme, which plays an important role in metabolism, is not produced or the produced form is not activatable.

Isoenzymes are distinguished by determining their enzymatic activity. This is done by measuring the differences in catalytic activity against substrate analogs or in the presence of inhibitors. Moreover, the catalytic activity of isoenzymes differs in regards to the stability toward denaturing reagents. As a rule, multiple enzymes do not show any differences in stability toward denaturing reagents.

Separative methods: A change in a small number of amino acid residues causes no, or only very minor, changes in the molecular weight of the isoenzymes. Therefore, chromatographic methods are not very useful in the differentiation of alloenzymes, but all the more so in the differentiation of multiple enzyme forms. If structural changes in isoenzymes cause a change in electric charge, agarose gel electrophoresis or isoelectrofocusing can be suitable separation methods. If there are variations in the carbohydrate side chains, lectin affinity chromatography can be useful.

Immunological analysis: Isoenzymes or multiple enzyme forms can differ in their antigenic determinants and be identified based on the binding of specific antibodies.

Clinical significance of isoenzymes and isoforms

The presence of isoenzymes and isoforms in serum increases the diagnostic sensitivity and specificity for the detection of organic diseases. The clinical conclusions are is described in the relevant articles on enzymes in this chapter.

1.1.1.3 Macroenzymes

Isoenzymes and isoforms are differentiated from enzymes characterized by multiplicity (multiple enzymes) that form based on post translational changes as a result of /67/:

The most common macroenzymes are immunoglobulin-associated (type 1 macroenzymes); all others are referred to as type 2 macroenzymes.

Immunoglobulin-associated enzymes: They are the most common form of macroenzymes and result from the formation of an immune complex between enzyme and autoantibody. This is a normal antigen-antibody reaction. The antigenic determinant of the enzyme binds to the Fab fragment of the antibody forming a macromolecular enzyme-immunoglobulin complex. The higher molecular weight with subsequently delayed clearance results in an accumulation in serum and elevated enzyme activity.

Some antibodies only react with a specific isoform of the enzyme, others react with all isoforms. The binding of the enzyme to the Fab fragment of the antibody stabilizes the enzyme’s activity in regards to thermal effects, influences the rate of elimination from the bloodstream and also has an effect on the enzyme kinetic characteristics. A slight inhibitory effect can be determined in many cases, whereas strongly inhibiting antibodies are rare.

Enzymes bound to other molecules: Complex formation is not only possible with autoantibodies, but also with molecules such as hydroxy ethyl starch, lipoproteins and α2-macroglobulin. This classification also includes oligomeric forms such as mitochondrial CK that passes into plasma in cellular necrosis. The biliary tract ALP, an alkaline phosphatase, is a different form of macroenzyme. It is bound to membrane fragments and detectable in serum in cholestasis.

Macroenzymes often persist for a long time, can cause elevated enzyme activity and thus simulate disease.

Clinical significance of the macroenzymes

Macroenzymes have a higher molecular weight than the free enzymes and therefore circulate in the plasma longer. Macroenzymes do not function as biomarkers of specific diseases. Elevated enzyme levels in serum caused by macroenzymes often lead to confusion among the treating physician and the laboratory and result in a multitude of further cost-intensive, unnecessary procedures. The significance of clinically important macroenzymes is shown in Tab. 1.1-2 – Macroenzymes: Characterization, clinical significance and laboratory findings.

Immunoglobulin-bound macroenzymes: macroforms have been described for the following diagnostically important enzymes: ALT, ALP, α-amylase, AST, CK, GGT, LD, lipase. Macroenzymes are rare events in healthy individuals, but if an enzyme level is pathologically elevated, it persists for a long time. The persistence of activity can remain almost unchanged for years. It is true that the concurrent occurrence of macroenzymes and autoimmune disorders has been described in individual cases. If detected, however, it must not be assessed as a specific and sensitive indication of a specific, manifested disease. There are no reliable indications that immunoglobulin-bound macroenzymes express an autoimmune disorder or that these circulating enzyme immune complexes themselves have a detrimental impact. The prevalence of macroenzymes generally increases with increasing age.

The fact that there are often more antibodies than the corresponding enzyme is another special characteristic of immunoglobulin-bound macroenzymes. Enzyme molecules released due to acute tissue damage can bind immediately to the free binding sites and be converted to the macroform. Thus, they may escape electrophoretic determination of the isoenzymes. On the other hand, the excess of antibodies results in competition for the enzyme molecule in the immunological enzymatic and isoenzymatic analysis; this may cause falsely low concentrations, especially in cases with short incubation periods.

Immunoglobulin-bound macroenzymes that are detected by coincidence in many cases only represent the tip of an iceberg; a much higher prevalence can easily be determined if they are selectively searched for. The detectability of macroenzymes in the blood of patients and healthy individuals increases as a function of the sensitivity of the detection procedure used. In these cases, however, the enzyme activities range within the reference interval. On this account, the prevalence given in the references often varies and seems contradictory at first glance.

Enzymes bound to other molecules: Macroforms have been described for the following diagnostically important enzymes: ALP, amylase, CK and GGT. The activity-time curve of this type of macroenzymes in many cases reflects the course of a disease. These macroenzymes can also be temporarily observed after therapeutic measures. Therefore, they may no longer be detectable if the disease improves or is cured. The determination of the prevalences for non-immunoglobulin-bound macroenzymes is even more strongly dependent on the detection procedure used and the selection of examined patients than for immunoglobulin-bound macroenzymes.

Unclear constellation of enzymes: It is important in all cases where the constellation of the enzymes does not match the clinical aspects to confirm or exclude the presence of macroenzymes. It often happens that elevated activities are prematurely classified as laboratory errors if no corresponding clinical correlate can be found. The verified presence of a macroenzyme can spare the patient from wrong diagnostic and therapeutic decisions. In particular, this applies to macro CK, which relatively often interferes with the determination of CK-MB.

1.1.1.4 Antibodies to tissue-specific enzymes

These autoantibodies circulate in blood and are directed against tissue-specific enzymes or regulators of specific enzyme activities /8/. The enzymes are expressed only in one tissue, for example against thyroid peroxidase, or in several tissues, for example against pyruvate dehydrogenase (Tab. 1.1-3 – Antibodies with regulating effects to the activity of tissue-specific enzymes). Macroenzymes often occur in older individuals and have no clinical significance in most cases, while antibodies to tissue-specific enzymes or their regulators show significant disease association.

1.1.2 Diagnostic information of enzymes

Indications of enzyme determination in serum or plasma include:

Information is gained from:

The level of enzyme activity is the resultant of several processes characterized by a typical time course. The following questions should be asked in the interpretation of an elevated enzyme level:

Location of the disease (organ localization)

The damaged tissue or organ can be localized by:

Tissue-specific enzymes: These are enzymes that occur exclusively in specific organs/tissues or occur there at very high activity compared to other organs/tissues. Increased presence in serum indicates the origin of the enzyme (Tab. 1.1-4 – Specific enzymes of important organs).

Isoenzymes: The tissue distribution of isoenzymes is genetically determined. Differentiation allows to determine the tissue where the elevated enzyme activity originated (e.g., pancreatic amylase, salivary gland amylase, myocardium-specific CK-MB or erythrocytic LD-1).

Enzyme pattern: Enzyme patterns can provide information regarding organ diagnosis based on the interrelation of enzyme activities. Aminotransferases are the basic enzymes of most enzyme patterns; the enzyme ratio is an indicatory criterion. More than 90% of all enzyme elevations are caused by the tissues of the liver, myocardium, skeletal muscles and erythrocytes. These tissues are significant for the differential diagnosis. The differentiation of the damage of one of the three tissues from liver injury is possible based on the CK/AST and LD/AST ratios (Tab. 1.1-5 – Differentiation of liver disease from other tissue damage).

Stage of the pathological process

Each mechanism that causes enzyme release to the blood and enzyme elimination from the blood shows a typical time course. The interaction of the different time courses results in characteristic activity-time curves. These curves can be used to derive a diagnostic time frame within which elevated enzyme activities are expected if the relevant disease is present. Moreover, the stage of the disease can be assessed based on this time frame.

If the organ is known, enzyme activities are usually higher in acute processes than in chronic ones. In acute organic diseases, the stage of the disease can also be determined from the ratio between enzymes with a short half-life and those with a long half-life. Differences in half-lives distort the organ-specific enzyme profile in serum and thus provide important information on the course of the disease. In acute hepatitis, for example, a declining AST/ALT ratio indicates remission of the hepatitis because the half-life of ALT is longer than that of AST.

Severity of cell damage

The severity is determined based on the ratio between structure-bound enzymes and enzymes dissolved in the cytoplasm (Tab. 1.1-6 – Enzyme pattern in acute severe tissue damage with cell necrosis). In milder damage, enzymes of the cytoplasm such as ALT and cytoplasmic AST are released. In severe damage with cell necrosis, the mitochondrial enzymes such as AST and GLD also pass into the plasma.

In liver disease, the extent of single cell damage is indicated by the AST/ALT ratio and the (AST + ALT)/GLD ratio. Values of the AST/ALT ratio above 1 or the (AST + ALT)/GLD ratio below 20 indicate acute severe hepatocellular damage. The enzyme pattern in serum in acute cell damage is similar to that of the tissue of origin.

Extension of cell damage

The level of enzyme activity and the integral below the activity-time curve, determined by 2–3 measurements within 24 hours for several days, correlate with the amount of tissue acutely damaged. High enzyme elevations indicate damage to major organs such as the liver or skeletal muscles.

Diagnosis of the disease

The enzyme pattern can provide decisive clues for diagnosis in patients with ambiguous acute clinical symptoms. If the pattern of CK, AST, ALT and lipase is determined in thoracic and/or abdominal pain, for example, it is with high probability that normal CK rules out myocardial infarction, normal ALT rules out acute liver disease and normal lipase rules out pancreatitis within a diagnostic time frame of 3–12 hours.

Differential diagnosis of the disease of an organ

In differential diagnosis, the ratio between the serum values of enzymes that are exclusively localized in defined structures or tissues of an organ and enzymes that occur in all cells of the organ with roughly the same activity is assessed, for example the behavior of GGT, ALP or GLD with reference to the aminotransferases in liver disease. The calculation of the ratio allows to differentiate between the following acute liver diseases:

GGT/AST

Differentiation between acute alcohol-toxic hepatitis (> 6) and acute viral hepatitis (< 1)

AST/ALT

Differentiation between acute obstructive jaundice (< 1) and chronic active hepatitis (> 1).

1.1.3 Enzymes in the differential diagnosis of acute diseases

In acute situations, the enzyme pattern of aminotransferases, CK, α-amylase/lipase, ALP and GGT provides information on the presence of important organic diseases. Several examples are listed below.

1.1.3.1 Differential diagnosis in acute thoracic and abdominal pain

Enzyme patterns for differential diagnosis in acute thoracic pain are shown in Tab. 1.1-7 – Enzyme pattern in acute thoracic or abdominal pain.

1.1.3.2 Enzyme patterns in liver disease

Enzyme patterns in acute and chronic liver diseases are shown in Tab. 1.1-8 – Enzyme pattern in acute liver diseases.

1.1.3.3 Enzyme activities in intensive care patients

Multi morbid patients and patients with sepsis, pneumonia, peritonitis, acute pancreatitis, postoperative or posttraumatic conditions, severe gastrointestinal complications, cardiac diseases including failure of the cardiac pumping function, persistent shock conditions or hematological diseases can show changed enzyme activities of these organs of origin despite primarily healthy liver and pancreas. Lack of perfusion of these organs is the cause in many cases (Tab. 1.1-9 – Median peak value of 100 critically ill patients with no primary liver disease, but with bilirubin values > 3 mg/dL (51 µmol/L)).

The mortality risk of critically ill patients is correlated with the presence of elevated liver enzyme activities on admission to the intensive care unit. Patients with elevated ALT, GGT or ALP up to twofold the upper reference limit on admission to the ICU have a lower chance of survival within 30 days (mean odds ratios: 2.7, 2.8, 3.9) than those without pathological levels. Episodes of artificial respiration or hemofiltration result in pathological ALT activities after three days (mean odds ratio: 2.7) /26/.

1.1.3.4 Enzyme activities in surgical interventions

This involves muscle enzymes in the first place and liver enzymes in the second (Tab. 1.1-10 – Incidence of elevated enzyme values after abdominal surgery). The maximum enzyme activity in interventions without complications is reached after 24–36 hours. The activity and duration of enzyme elevation are dependent on the nature and extent of intervention.

In courses without complications, the levels return to normal within 1 week. In abdominal interventions, elevated activities were measured for CK in 76% and for AST in 50% of the cases. The activities of CK were elevated up to seven-fold the upper reference limit (median: 2.1-fold) and those of AST were elevated up to 3.5-fold (median: 1.2-fold) /27/.

1.1.3.5 Enzymes in cerebral seizures

Grand mal seizures are regularly associated with elevated CK. The activity in idiopathic grand mal seizure is up to 6-fold the upper reference limit; much higher levels are observed in grand mal seizure after alcohol withdrawal, and 50–100-fold elevated levels are measured in the epileptic state. Peak values are reached within 1–3 days; levels decline to within the reference interval after 4–10 days. After the epileptic state, the activity pattern of CK, LD and AST corresponds to that in myocardial infarction; the ALT can also be elevated. Patients suffering idiopathic grand mal seizure do not have a uniform enzyme pattern /28/. The CK isoenzymes CK-MB and CK-BB do not show pathological levels.

1.1.3.6 Enzymes in cancer

Elevations of enzyme activities in serum measured in tumor diseases are dependent on the stage of the tumor. However, the enzymes are not suited for use as a screening method for malignant tumors. Organ-specific enzymes such as GGT or the so-called ubiquitous enzymes can be elevated /29/. The latter belong to the large group of glycolytic enzymes such as LD. They are involved in the metabolism of the cell and ubiquitous in all organs. Enzyme elevations occurring in tumor diseases can be based on:

The behavior of enzymes in carcinoma patients is shown in Tab. 1.1-11 – Enzymes in malignant diseases.

1.1.4 Biological influence factors and interference factors

Elevated or low enzyme activities can be due to biological influence factors and interference factors affecting the relevant assay /24/. Biological influence factors lead to changes in the enzyme activity in serum in vivo, i.e., already before blood sampling, while interference factors change the result in vitro (Tab. 1.1-12 – Factors interfering with the serum enzyme determination).

1.1.4.1 Biological influence factors

Important biological influence factors causing changes in enzyme activity include diagnostic and therapeutic measures, food intake, alcohol, physical exertion, pregnancy, body position and constriction method during blood sampling as well as post translational changes in the enzyme such as macroenzyme formation.

Food intake

Elevations of the ALT activity by 10% and the AST activity by 20% compared to the initial level can occur two hours after a generous lunch; the ALP activity can also be elevated significantly. The elevation of ALP is especially pronounced in individuals with blood groups 0 and B and Lewis-positive.

Blood sampling

Posture and tourniquet application have a clinical relevant effect on the serum enzyme activity when the levels are in the upper reference interval. If the blood samples are collected with the patient in a sitting position after seating for at least 15 min. (the normal office situation), the enzyme values are 5–10% higher. Tourniquet application for more than 2 min. has the same effect so that the addition of both biological factors can lead to an increase in enzyme activity of 10–20% /32/. Compression of the vein for 6 min. leads to an increase of 8–10% in lipase, ALT, CK, GGT and LD by 8–10% /33/.

Intraindividual variation

No significant clinically relevance in diurnal variations of the serum enzymes have been found.

In a study /34/, the following values for the coefficient of variation (CV) were determined for the intraindividual variance within 6 months: CK 22.8%, ALT 30%, AST 12.2%, LD 10.3%, GGT 12.9%, ALP 7.4%.

Age dependency

The following age-related differences have been described for some enzymes /35/:

Physical exertion

Muscle activity causes elevated enzyme activities, especially for CK, AST and LD. The level, duration and frequency of the elevation are dependent on the physical condition. The increase follows the pattern CK > AST > LD; levels usually return to normal within a week /36/.

In bodybuilders, for example, 5-fold elevated CK and 2-fold elevated AST activities have been reported. The ALT elevates further upon the intake of anabolics.

On the third day during an ultra-long distance run of 50 klometers per day for 20 days, the athletes show an average elevation of CK to 20-fold, CK-MB to 2-fold and AST to 3-fold the upper reference interval value. Afterwards, until the end of the run, the CK decreases to 8-fold the upper reference interval value and CK-MB and AST return to levels within the reference interval /37/.

Nutrition

Prolonged fasting as well as high protein intake can result in elevated aminotransferases. The LD can increase after high-fat diet and decrease after low-fat diet. Individuals with blood groups 0 and B and Lewis-positive show elevated ALP after a high-fat meal due to the pronounced increase in intestinal ALP.

Pregnancy and oral contraceptives

Working pregnant women can have elevated CK, especially CK-BB. Oral contraceptives in doses corresponding to those of the micro pill usually do not cause elevated enzyme levels. Enzyme induction has been described for ALP and GGT if the micro pill contains ethinylestradiol /38/.

Alcohol

Depending on the consumed quantity and duration of consumption, alcohol causes elevated GGT levels and with additional liver injury also elevated ALT, AST and GLD. The elevation can be considerable if the alcohol is consumed during or after physical exertion. The enzyme increase in alcoholism follows the pattern GGT > AST, ALT > GLD.

Drugs

Drugs can cause elevated enzyme activities due to enzyme induction or tissue damage (Tab. 1.1-13 – Drugs governing the rate of enzyme-catalyzed reactions).

1.1.4.2 Interference factors

Drugs, hemolysis, hyperbilirubinemia, hyperlipidemia, metabolites of the sample and anticoagulants are key interference factors that can cause a change in enzyme activity.

Metabolite-induced interferences

Pyruvate concentrations of the sample higher than 1,100 μmol/L inhibit the optical assay through NADH2 consumption in the preincubation step /39/. Falsely normal activities of AST, ALT and GLD are measured. The pyruvate passes from the erythrocytes into the serum if the erythrocytes are separated many hours later.

Drugs

Drugs have little effect on in-vitro kinetic enzymatic analysis. A detailed round-up of references is presented in Ref. /404142/.

Hyperbilirubinemia

Hyperbilirubinemia usually does not interfere with kinetic enzymatic analysis. In a study /43/, in which the bilirubin concentration in samples was 29.2 mg/dL (500 μmol/L), the levels of ALP, ALT, AST, α-amylase, CK, GGT and LD were determined on 16 automatic analyzers. The measurement of AST was interfered on three and that of ALT on two automatic analyzers and that of LD on one automatic analyzer.

Hemolysis

Hemolysis interferes with kinetic enzymatic analysis depending on the concentration. In a study /43/, in which the concentration of free hemoglobin in samples was 2.4 g/L (240 μmol/L), the activities of ALP, α-amylase, CK and GGT were determined on 16 clinical chemical analyzers. Interferences with the measurement of ALP was found in 8 test systems, with the CK in 9 and with the measurement of GGT in 3.

Hypertriglyceridemia

Hypertriglyceridemia usually does not interfere with kinetic enzymatic analysis on automatic analyzers up to a concentration of 610 mg/dL (700 μmol/L) /43/.

Anticoagulants in diagnostic samples

All enzymatic analyses can be performed in serum and in heparin-anticoagulated plasma. The determination of ALT, AST, CK, GLD and LD is also possible in EDTA plasma. Citrate plasma should not be used for enzymatic analysis because there is only insufficient data available on interference factors /44/.

Enzyme stability during storage /45/

In sera separated from the clot, ALP, α-amylase, ALT, AST, CK, CHE, GGT and LD remain stable for at least 4 days at 9 °C and, at a temperature of 20 °C, ALP, α-amylase, ALT, AST and CHE remain stable for 3 days.

References

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2. Moss DW. Nomenclature and units in enzymology. In: Bergmeyer HU, ed. Methods in enzymology, vol 1. Weinheim, VCH 1981: 7–21.

3. Haar HP, Netheler H, Ziegenhorn J. Absorption photometry, nephelometry, turbidimetry. In: Bergmeyer HU, ed. Methods in enzymology, vol 1. Weinheim, VCH 1981: 280–305.

4. IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C. Part 1–7. Clin Chem Lab Med 2002; 40: 631–745.

5. IUPAC-IUB Commission on Biochemical Nomenclature. Nomenclature of Multiple Forms of Enzymes. Recommendations 1976. J Biol Chem 1977; 252: 5939-41.

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7. Sturk A, Sanders GTB. Macroenzymes: prevalence, composition, detection and clinical relevance. J Clin Chem Clin Biochem 1990; 28: 65–81.

8. Kiechle FL, Quattrociocci-Longe TM, Brinton D, Gordon S, Sykes E, Elkhalifa MY. Autoantibodies to specific enzymes: a review. Ann Clin Lab Sci 1996; 26: 195–207.

9. Wenham PR, Chapman B, Smith AF. Two macromolecular complexes between alkaline phosphatase and immunoglobulin A in a patient’s serum. Clin Chem 1983; 29: 1845–9.

10. Mifflin E, Bruns DE. University of Virginia Case Conference. Macroamylase, macro creatine kinase, and other macroenzymes. Clin Chem 1985; 31: 1743–8.

11. Zaman Z, van Orshoven A, Marien G, Fevery J, Blanckaert N. Simultaneous macroamylasemia and macrolipasemia. Clin Chem 1994; 40: 939–42.

12. Stasia MJ, Suria A, Renversez JC, Pene F, Morel-Fermiez A, Morel F. Aspartate aminotransferase macroenzyme complex in serum identified and characterized. Clin Chem 1994; 40: 1340–3.

13. Krishnamurthy S, Korenblat KM, Scott MG. Persistent increase in aspartate aminotransferase in an asymptomatic patient. Clin Chem 2009; 55: 1573–7.

14. Tameda M, Shiraki K, Ooi K, Takase K, Kosaka Y, Nobori T, et al. Aspartate aminotransferase-immunoglobulin complexes in patients with chronic liver disease. World J Gastroenterol 2005; 11: 1529–31.

15. Caropreso M, Fortunato G, Lenta S, Palmieri D, Esposito M, Vitale DF, et al. Prevalence and long-term course of macro-aspartate aminotransferase in children. J Pediatr 2009; 154: 744–8.

16. Laureys M, Sion JP, Slabbynck H, Steenssens L, Cobbaert C, Derde MB, et al. Macromolecular creatine kinase type 1: a serum marker associated with disease. Clin Chem 1991; 37: 430–4.

17. Davidson DF, Scott JG. Detection of creatine kinase isoenzymes. Ann Clin Biochem 2012; 49: 482–5.

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1.2 Biomarkers of liver disease

Lothar Thomas

Elevated liver enzymes can have a multitude of causes and causative factors. As a rule, a disease at hand can be diagnosed based on the medical and medication history, clinical examinations with upper abdominal sonography and laboratory diagnostic findings.

Besides diagnosing, biomarkers are useful to differentiate between acute and chronic hepatopathy, assess the severity, assist etiological verification, draw prognostic conclusions and perform therapy monitoring.

General clinical liver-associated tests

The following important general tests and analyses primarily give a direction to further procedure in many cases, based on their constellation and taking into account the medical and medication history /1/:

1.2.1 Determination of extrahepatic factors

The enzymes analyzed in general clinical tests can also be elevated in hepatic co-reactions within the scope of extrahepatic and systemic diseases. This can be the case, for example, in pancreatitis, exogenous-toxic, exogenous-allergic, autoimmune, vascular and metabolic diseases.

Assays: Blood count, albumin, serum protein electrophoresis, cholesterol, triglycerides, HbA1c, ferritin /1/.

Complementary investigations /1/

If the general clinical liver-associated tests indicate a liver disease, further assays are required for differentiation.

Assays: HBsAg, anti-HCV, IgG, IgA, IgM, ANA, AMA, SMA, LKM-Ak, SLA, pANCA (see Chapter 25 – Autoimmunity and autoantibody testing), ceruloplasmin, Cu in 24 h urine, HFE mutation, α1-antitrypsin genotype.

Chronic liver disease

Chronic liver diseases are usually asymptomatic. ALT and GGT are moderately elevated to 2–5-fold the upper reference limit. One should keep in mind in differential diagnosis that, according to investigations in the U.S.A., elevated ALT occurs in 8% of the normal population and 70% of these cases are primarily unclear. The main cause seems to be fatty liver in the form of non-alcoholic steatohepatitis (NASH) in adiposity and metabolic syndrome, and not the non-alcoholic fatty liver (NAFL) /2/.

Inflammation and fibrosis are the essential characteristics of chronic liver disease. Classification into stages is based on the assessment of the progressive deposition of fibrotic extracellular matrix (ECM), also referred to as fibrogenesis. The qualitative composition of ECM (various types of collagen, proteoglycans, structural glycoproteins, hyaluronic acid) and their spatial distribution within the liver are subject to significant variation.

In addition, the stage is determined based on compensatory regenerative processes causing changes in the anatomic structure.

Liver biopsy is the gold standard for the assessment of fibrosis. Information regarding fibrotic transformation can also be obtained from biomarkers (increase in De Ritis ratio, thrombocytopenia, hypergammaglobulinemia, cytokeratin-18 fragments). Fibrosis staging scores have been developed because of the low diagnostic value of the individual parameters (Tab. 1.2-1 – Hepatic fibrosis staging based on scores and serum markers).

Fatty liver

The following are distinguished from alcoholic fatty liver:

Liver cirrhosis

Liver cirrhosis is the final stage of many chronic liver diseases progressing for years or decades /3/. It is characterized by lobular transformation of the parenchyma with septal fibrosis, infiltration of inflammatory cells and a change in the vascular bed. The progression of liver cirrhosis is governed by its etiology. The main causes of liver cirrhosis are alcoholic and non-alcoholic fatty liver disease, hepatitis B, hepatitis C and the combination of hepatitis C and alcohol abuse. Increasing structural changes of the tissue lead to a loss of function and portal hypertension. Vascular dysfunction results in the increased release of vasoconstrictive hormones. Imminent complications include: intestinal hemorrhage, ascites, encephalopathy and hepatocellular carcinoma /5/.

Hepatocellular carcinoma (HCC)

The majority of hepatocellular carcinomas arise in a background of cirrhosis. The risk of carcinoma depends on the present liver disease and is /3/:

Laboratory findings

According to laboratory test results in alcoholic fatty liver, GGT is elevated higher than ALT. These ratios are inverted in NASH associated with elevated enzyme levels. Liver enzymes are usually not elevated in NAFL. Findings in chronic liver disease with transition into liver cirrhosis include mildly elevated aminotransferases, hypoalbuminemia, plasma thrombine time extension, reduced cholinesterase and hyperbilirubinemia. Advanced liver disease with transition into cirrhosis is indicated by thrombocytopenia.

Cytokeratin-18 fragments (CK-18) are detectable in serum and act as a fibrosis marker of NASH. In a study /4/, the mean CK-18 values of controls were 145 U/L (25th to 75th percentile 126–190) and those of patients with NASH were 244 (161–427) U/L. Expressed as odds ratio, the risk of NASH increased by 30% with every increase by 50 U/L.

1.2.2 Scores: Liver failure, non-alcoholic fatty liver disease

Liver failure can be acute or based on irreversible chronic liver disease. Orthotopic liver transplantation is the only causal therapy of liver failure /6/.

Chronic diseases causing liver failure include: alcohol-toxic liver cirrhosis, viral and autoimmune hepatitides, cholestatic liver diseases, malignomas, metabolic disorders and genetic disorders (Wilson’s disease, hemochromatosis, α1-antitrypsin deficiency, urea cycle disorders, storage diseases).

Acute liver failure is potentially reversible. Acute paracetamol intoxication and acute hepatitis B infection are the main causes of acute liver failure. Orthotopic liver transplantation is the therapy option for the prognostic assessment and selection of patients with irreversible liver failure. Scoring systems are available to identify indications (Tab. 1.2-2 – Criteria for orthotopic liver transplantation in acute liver failure).

The Model for Endstage Liver Disease (MELD) score has been established in the Eurotransplant region to regulate organ allocation. It is based on the determination of bilirubin and creatinine in serum and International Normalized Ration (INR) in citrated blood.

MELD/PELD score /7/

The Model for End-stage Liver Disease (MELD) score for adults and the Pediatric End-stage Liver Disease (PELD) score for children serve as indicators for the urgency of orthotopic liver transplantation. An estimate of the three-month mortality in the end stage of chronic liver disease is possible.

Calculation of the MELD score

Score = 3.8 × LN [bilirubin (mg/dL)] + 11.2 × LN [INR] + 9.6 × LN [creatinine (mg/dL) + 6.4]

or

Score = 3.8 × LN [bilirubin (μmol/L)] + 11.2 × LN [INR] + 9.6 × LN [creatinine (μmol/L) – 53.77]

Calculation of the PELD score

Score = [0.436 × age] – [0.687 LN albumin (g/dL)] + [0.48 × LN bilirubin (mg/dL)] + [1.857 × LN INR] + [0.667 × growth delay (< 2 SD)]

LN = natural logarithm. If, in the MELD score, creatinine is ≤ 1 mg/dL, the value 1 is substituted.

Assessment of MELD scores and PELD scores: The validity of the MELD score for assessing the prognosis of liver failure and the prognosis after transplant is shown in Tab. 1.2-3 – Mortality rate (%) after 3 months as a function of the MELD score. For assessment, the PELD score is transformed into the MELD score using an equation /7/.

Prognosis of paracetamol-induced liver injury /8/

Determine the α-fetoprotein (AFP) on a daily basis for 7 days from the point in time at which the ALT exceeds 1000 U/L. Survivors show elevated AFP in the median on day 1, non-survivors only after 4.1 days. An AFP level of not more than 3.9 μg/L on day 1 identifies non-survival (diagnostic sensitivity of 100% at 74% specificity, positive predictive value: 45%, negative predictive value: 100%). Refer to Tab. 1.2-4 – Modified Child-pugh score.

Non-alcoholic fatty liver disease (NAFLD) fibrosis score

The term non-alcoholic fatty liver disease covers cases of a wide spectrum of severity, ranging from bland fatty liver without any inflammation and with little or no tendency to progress all the way to non-alcoholic steatohepatitis (NASH) with inflammatory reactions and hepatocyte damage, with or without fibrosis. Between 5 and 20% of patients with fatty liver develop NASH over the clinical course; in some 10-20% this develops into higher-grade fibrosis, in 5% this is progressive to full-blown cirrhosis. The NAFLD fibrosis score should be performed for diagnosis. The score is computed on the basis of the parameters age, body-mass index, diabetes status , ASAT ALAT, platelet count and albumin level. The positive predictive value is 82% to 90% and a negative predictive value is 88% to 93% /910/.

Hepatopathies and biomarkers

For the clinical and laboratory findings in acute and chronic hepatopathies refer to

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1.3 Alkaline phosphatase (ALP)

Lothar Thomas

Alkaline phosphatase (orthophosphoric-monoester hydrolase) is a cell membrane-bound enzyme expressed in all tissues. ALP in serum represents the activity of multiple forms of the enzyme. More than 17 isoforms are of ALP are detectable by use of an isoelectric focusing technique. Four genetically encoded variants of ALP have been identified /1/:

The three tissue-specific isoenzymes intestinal ALP, placental ALP and germ cell ALP

The genes of the tissue-specific isoenzymes primarily occur in the tissues after which they are named. The tissue-nonspecific gene is expressed by various tissues. The products of this gene are subject to post translational modification in glycosylation as a result of which isoforms such as the liver ALP, bone ALP and kidney ALP are formed. In all, at least 15 ALP isoforms have been identified. The gene of the placental ALP exists in numerous allelic modifications.

In every tissue, ALP shows a certain extent of microheterogeneity in terms of molecular structure and size that depends on the glycation pattern. Moreover, ALP can be present as macroenzyme or as particulate ALP bound to membrane fragments.

The liver ALP, bone ALP and intestinal ALP can be detected in the serum of healthy individuals by using conventional assay methods. The high performance liquid chromatography with post-column reaction detection allows to determine six ALP isoforms in the serum of healthy individuals: bone/intestinal ALP, two bone ALPs and three liver-ALPs /2/. They mainly differ in the sialic acid content of their carbohydrate side chains.

The determination of total ALP is performed routinely. Even if the total ALP is normal, ALP isoenzymes are determined to enhance diagnostic sensitivity and specificity at specific diagnostic requirements. The most common requirement is to differentiate between the isoforms liver ALP and bone ALP in elevated total ALP.

Alkaline phosphatase in malignant tumors

The tissue-specific isoenzymes placental ALP and germ cell ALP can be increasingly expressed in malignant tumors. They are also known as “Regan-type ALP". Their expression in tumor cells suggests that they are oncofetal proteins involved in tumor genesis. Tumors expressing these isoenzymes are differentiated as follows:

The placental ALP produced by cells of the syncytiotrophoblasts can be ectopically expressed in carcinomas. It is also referred to as Regan-type ALP because it was primarily detected in a lung carcinoma patient named Regan. The biochemical behavior of the Regan ALP is similar to that of the placental ALP with a few exceptions. It is detected in seminomas, in ovarian, uterine and pulmonary cancer, in malignant tumors of the gastrointestinal tract, hypophysis and thymus.

1.3.1 Indication

Total ALP

ALP isoenzymes

The diagnostic value of total ALP is sufficient in numerous clinical requirements. If the total ALP is elevated, the determination of isoenzymes, especially the bone ALP, allows conclusions as to the tissue or organ of origin.

The determination of the bone ALP is indicated /3/:

1.3.2 Method of determination

1.3.2.1 Total ALP (orthophosphoric- monoester phospho hydrolase, EC 3.1.3.1)

Method of the International Federation of Clinical Chemistry (IFCC) /4/

Principle: The determination of the catalytic concentration of ALP in serum depends on the chosen measurement parameters. Especially the choice of the buffer is of great importance. The phosphomonoesterase activity of ALP is determined using 4-nitro phenyl phosphate (NPP) as a substrate. In the presence of 2-amino-2-methyl-1-propanol (AMP), ALP acts as phospho transferase and transfers a phosphate group of NPP to AMP, which, in turn, catalyzes the dephosphorylation of the substrate. The amount of colored product (NP) formed per time unit, measured as absorption increase at 405 nm, is an indicator of the catalytic activity of ALP (Tab. 1.3-1 – Principle of ALP determination). The reaction process is started by adding the substrate.

1.3.2.2 ALP isoenzymes and isoforms

Numerous methods for the determination of isoenzymes and isoforms of the ALP have been described in the past 30 years. More than 15 isoenzymes and isoforms are differentiated by different methods /2/. The differentiation of elevated total ALP by liver ALP and bone ALP is important in clinical routine diagnostics and can be performed by electrophoresis. The quantitative determination of bone ALP is performed by immunoassays or lectin precipitation. The placental isoenzyme is determined quantitatively by immunoassay.

Electrophoretic differentiation

Separation following neuraminidase treatment: Before electrophoretic separation, serum is incubated with neuraminidase. This enzyme removes negatively charged sialic acid residues from the surface of the bone ALP faster than from that of the liver ALP.

The fractionation of the ALP isoforms toward the anode on the carrier medium polyacrylamide or agarose under alkaline buffer conditions slows down the electrophoretic mobility of bone ALP in relation to liver ALP. This allows to differentiate between liver ALP and bone ALP. Separation by electrophoresis in untreated serum yields insufficient results. Semi quantitative evaluation is performed densitometrically based on the isoform activities visualized on the carrier medium.

Lectin affinity electrophoresis /5/: Using carrier medium containing wheat germ lectin (cellulose acetate sheet, agarose gel), serum is fractionated under alkaline buffer conditions to migrate toward the anode. Wheat germ lectin binds the bone ALP and thus makes it less mobile. As a result, it remains near the location where it was applied and is separated from the other ALP isoforms, especially liver ALP. Semi quantitative evaluation is performed reflectometrically based on the isoform activities visualized on the separation sheet.

Quantitative determination of bone ALP

Lectin precipitation /6/: First, the total ALP is determined. Then the bone ALP is precipitated using a precipitating agent, a wheat germ lectin, and the residual activity is subsequently measured in the supernatant. The activity of bone ALP is obtained by calculating the difference.

ELISA for bone ALP determination /7/: The serum sample is incubated with a buffer in the well of a micro titer plate coated with monoclonal antibodies to bone ALP. After removal of the non-bound material, the substrate p-nitrophenyl phosphate is added and the antibody-bound enzyme activity is determined by photometry.

Immunometric assay for bone ALP determination /8/: This is a solid-phase assay in a two-step process. A specific determinant of the bone ALP in the sample reacts with the monoclonal antibody on a sphere (solid phase). At the same time, a second specific determinant of the bone ALP reacts with a second, radioactively labeled or enzyme-labeled monoclonal antibody forming a sandwich of solid phase, bone ALP and labeled antibody. After washing the sphere, the solid phase-bound radioactivity or enzyme activity are measured. Lower detection limit: 2 μg/L.

Quantitative determination of placental ALP

ELISA for activity determination /9/: The serum sample is incubated with a buffer for 3 hours at 37 °C in the well of a micro titer plate coated with monoclonal antibodies to human placental ALP. After removal of the antibody-unbound sample parts in a washing step, the serum is incubated with substrate solution (p-nitrophenyl phosphate) and the enzyme activity is subsequently determined by photometric measurement of the formed p-nitro phenolate at 405 nm. Lower detection limit: 30 mU/L.

1.3.3 Specimen

Serum or heparin anticoagulated blood; no EDTA, citrate or oxalate plasma: 1 mL

1.3.4 Reference interval

See Tab. 1.3-2 – Reference interval of ALP.

1.3.5 Clinical significance

1.3.5.1 Elevated activity of total ALP

In healthy adults, the ALP measurable in serum or plasma consists of approximately equal proportions of liver ALP and bone ALP. In children up to 15 years of age, the proportion of the bone isoform in the ALP activity is as high as 80%. About 25% of healthy individuals also have intestinal ALP that accounts for approximately 10% of the ALP activity under fasting conditions. The proportion of other ALP isoenzymes or isoforms in the ALP activity is below 5% /14/.

Elevated ALP can have physiological causes or be based on diseases of the liver or skeletal system. The leukocytes and kidneys also release ALP into circulation, but not in quantities that lead to ALP elevations above the upper reference limit.

Rising or elevated levels of total ALP and its isoenzymes and isoforms can have the following physiological causes:

Pathologically elevated total ALP and/or ALP isoenzymes or isoforms can have the following causes:

The determination of isoenzymes and isoforms of ALP in cases of elevated total ALP or activities still within the reference interval can provide the following information:

Diseases of the liver and bile ducts

Diseases of the liver and bile ducts are the most common causes of elevated total ALP. The enzyme is pathologically elevated in about 60% of diseases of the liver and bile ducts. In a pattern together with AST, ALT and GGT, ALP is of differential diagnostic significance for the detection of cholestatic conditions. Compared to aminotransferase activity, the ALP is high in cholestasis and normal or mildly elevated in the absence of the cholestatic component. The diagnostic sensitivity of ALP is 80–100% in cholestatic liver disease and only 25% in alcoholic liver injury /21/. Therefore, in liver diseases with high GGT, the level of total ALP is a good diagnostic criterion for differentiating between alcoholic damage and cholestatic processes. No or relatively mild elevations of total ALP compared to GGT are indicative of alcoholic damage. Elevated ALP is also detected in metastatic and infiltrative liver diseases such as leukemia, lymphoma or sarcoidosis.

Drug-induced toxic liver injury can imitate almost the entire spectrum of liver diseases. However, acute hepatitis is the most common form with an incidence of about 90%. Drug-induced toxic hepatitis is subdivided into three forms based on the determination of ALT and ALP /22/:

Diseases of the skeletal system

Total ALP is commonly used as a biomarker in suspected disease of the skeletal system. However, the lack of diagnostic sensitivity and specificity is a disadvantage of this method. Hence, total ALP is only elevated in significant involvement of the skeletal system, as for example in Paget’s disease, vitamin D deficiency rickets, metastatic bone formation or lytic lesions and primary hyperparathyroid disorder. Total ALP is elevated only occasionally in osteopenic and osteoporotic osteopathies. In these cases, the determination of bone ALP, especially in monitoring, is of diagnostic significance /23/. This is because the bone ALP, like osteocalcin, indicates bone formation, whereas N-terminal pro peptide (PINP) and carboxy-terminal cross-linked telopeptides (β-crosslaps) are products of bone resorption. However, since bone resorption and bone formation are linked, the biomarkers of both processes behave concordantly and assume similar in many cases.

Exceptions from this rule can be found in glucocorticoid treatment during which bone formation is acutely inhibited and bone resorption is enhanced. In anabolic therapy, bone formation is enhanced and bone resorption remains unaffected /2425/.

Malignant tumors

Significant elevations of total ALP can be measured in patients with malignant tumors. In many cases, the determination of the ALP isoenzymes or isoforms confirms the metastatic spread of the tumor to specific tissues. For example, elevated bone ALP in prostate carcinomas indicates metastatic spread to the skeletal system, elevated liver ALP in colon carcinoma indicates hepatogenic metastasis and elevated levels of both isoforms in lung carcinoma indicate metastasis in both organs.

The ALP isoenzymes placental ALP and Regan-type ALP fulfill the essential criteria of a tumor marker in patients with germ cell tumors of the testes. The homology of the two isoenzymes is 98%; therefore, they are often referred to as being synonymous. The Regan-type ALP is detected in serum in testicular, ovarian, pulmonary, bladder and gastrointestinal tumors /20/.

Kasahara ALP is a multiple ALP, which – in biochemical terms – is a heterodimer of placental ALP and intestinal ALP and cannot be determined with commercially available test kits. It is detected in hepatocellular carcinoma and renal cell carcinoma.

Tumor patients occasionally show unknown variants of ALP isoforms that cannot be determined in detail.

Elevated ALP may also be caused by ALP isoenzymes complexed with immunoglobulins (see also Tab. 1.1-2 – Macroenzymes: Characterization, clinical significance and laboratory findings/26/.

Cardiometabolic diseases

In the United States National Health and Nutrition Examination Survey (NHANES) 2005–2006, the level of total ALP was significantly correlated with age, hip circumference, body mass index, blood pressure, physical exertion, ethnic origin and triglyceride levels. Compared to the lowest quartile of ALP, individuals with the highest quartile increasingly showed cardiovascular diseases (odds ratio: 1.9) as well as high blood pressure, hypercholesterolemia and diabetes mellitus (odds ratio: 1.7). It is assumed that the ALP, similarly to CRP, acts as a cardiometabolic biomarker and has higher levels in atherosclerosis and peripheral vascular disease /27/.

1.3.5.2 Reduced ALP activity

Low ALP levels in serum are rare and have an incidence of about 0.2% in clinical patients (Tab. 1.3-7 – Diseases associated with low ALP levels).

Hereditary hypophosphemia, a significant form of reduced ALP activity, can be associated with low total ALP and skeletal diseases due to lack of expression of tissue-nonspecific ALP /28/.

1.3.6 Comments and problems

Complexing substances such as citrate, EDTA or oxalate bind cations such as zinc and magnesium, which are important cofactors for ALP activity. The ALP activities measured in such anticoagulated plasma samples are falsely low /73/. This is also the case in samples taken after administration of blood transfusions because infused citrate causes decrease of enzyme activity.

Twelve-hour fasting is necessary prior to blood sampling because elevated total ALP levels of 30 U/L on average can occur 2–4 hours after food intake due to intestinal ALP entering the circulation. The fasting intestinal ALP in diabetics was 11–79 U/L and postprandially increased to 41–106 U/L /74/. The activity of intestinal ALP is elevated after high-fat meals.

Hemolysis

Hemoglobin inhibits the activity by about 3% /73/.

Half-lives

Drugs

Drugs can have an elevating or lowering effect on ALP activity /75/.

Elevating effect: Allopurinol, amsacrine, carbamazepine, cotrimoxazole, cyclophosphamide, disopyramide, erythromycin, gold salts, isoniazid, ketoconazole, mercaptopurine, methotrexate, methoxyflurane, α-methyldopa, methyltestosterone, oxacillin, oxyphenisatine, papaverine, penicillamine, perhexiline, phenobarbital, phenylbutazone, phenytoin, primidone, propylthiouracil, ranitidine, trimethoprim/sulfamethoxazole, sulfasalazine, valproate, verapamil.

Lowering effect: Clofibrate, oral contraceptives.

Stability in serum

At 20 °C activity reduced by 3 elevated% after 3 days; at 4 °C no reduced activity within 1 week /76/.

Quality assurance

The ALP level can increase within a period of several hours after the lyophilized control sera are dissolved, depending on the lyophilized ALP isoenzyme. The reconstitution times specified by the manufacturer must be adhered to.

Method of determination of ALP isoenzymes

ELISA for activity determination: Cross-reactivity of 3–8% if the total ALP is pathological /855/.

Immunometric assay: The cross-reactivity of bone ALP and liver ALP can be as high as 16%. Only the liver ALP should be elevated if the disease is hepatobiliary and not skeletal. Under this condition, the immunometric assay does not yield a pathological bone ALP result until the total ALP is 2.6-fold elevated /77/.

Electrophoretic separation in carrier medium containing wheat germ lectin: This method shows the same precision and accuracy for the bone ALP and liver ALP as the precipitation method. Smearing of the bone ALP band toward the anode occurs in high bone ALP levels.

Age dependency

The total ALP remains approximately constant up the 10 years of age, then increases continuously and reaches the highest median level at 14–16 years of age. This peak level can be up to 4-fold the upper reference limit of adults in girls and up to 5-fold the upper reference limit of adults in boys /17/. After 20–25 years of age, the levels of the two genders converge and remain constant in men until death /73/.

Women show menopausal elevations of the total ALP by 30–60% due to increasing bone ALP; the upper reference limit is usually not exceeded /78/.

1.3.7 Pathophysiology

The ALP is a membrane-bound enzyme localized in all tissues. It binds to the outer surface of the cell membrane through a carboxy-terminal phosphatidylinositol glycan anchor. The membrane-bound form is a tetramer that is detached by the phospholipases C and D and then enters the blood circulation. Here, the ALP occurs as a dimer with two active centers, containing two zinc atoms and one magnesium atom each.

The ALP consists of a group of isoenzymes encoded by four gene loci. The gene of the tissue-nonspecific isoenzyme (Tissue Non Specific Alkaline Phosphatase; TNSAP) is located on the short arm of chromosome 1, the genes of the tissue-specific enzymes intestinal ALP,.placental ALP and germ cell ALP are located on the long arm of chromosome 2. The TNSAP gene is expressed in many tissues such as liver, bone or kidney; the ALPs produced by these organs/tissues are isoforms differing due to post translational modification /14/. The isoforms have an identical primary protein structure, but differ in regards to their extent of sialylation. This results in changes in electrophoretic mobility, stability to heat and the inhibitory effect of certain chemicals. For example, the placental isoenzyme can be differentiated from the liver-specific, bone-specific and kidney-specific isoforms based on activity inhibition by L-phenylalanine and heat stability at 65 °C for 10 minutes.

The specific activity of the ALP measured in U/g of tissue is 3,214 in the placenta, 2,524 in the small intestine, 619 in the kidney, 571 in bone and 100 in the liver.

Artificial, high-concentration substrates are used for determining the ALP. However, pyrophosphate, phospho ethanolamine and pyridoxal-phosphate are the natural substrates of plasma ALP The concentration of inorganic phosphate is a natural regulator of ALP activity in plasma. At normal phosphate concentrations, the ALP activity is inhibited by 50% compared to pyridoxal-phosphate, decreases as a function of increasing phosphate concentrations and rises as a function of decreasing concentrations /79/.

1.3.7.1 Liver ALP

Liver ALP is produced on all levels of the biliary tract system from the bile canaliculi in the liver to the mucosa of the gall bladder and the large bile ducts. Any obstruction of the bile flow, be it in the bile canaliculi or in the minor duodenal papilla, causes the induction of liver ALP in the bile ducts. The mediator of this enzyme induction is unknown. The ALP and bilirubin usually behave concordantly in serum if, for example, the bile duct is obstructed as in occlusion by a biliary calculus or in carcinoma of the head of pancreas. However, if only the right hepatic bile duct is obstructed, bilirubin and ALP do not behave concordantly. In this case, ALP is elevated, but bilirubin is normal. This is due to the presence of intrahepatic anastomoses of the biliary ducts that allow bilirubin excretion through the left hepatic duct. Isolated elevations of ALP with normal aminotransferases also occur in infiltrative liver diseases such as tumors and granulomas, but macro ALP should also be considered (see Section 1.1.2 – Diagnostic information of enzymes). Elevated ALP occurs if a bile duct is compressed and the bile flow is obstructed due to metastases, tumors or granulomas.

1.3.7.2 Bone ALP

Bone ALP is localized on the osteoblast cell membrane. Increased osteoblast activity causes an increase in the enzyme level. Bone ALP is immediately involved in bone mineralization as demonstrated by findings on hereditary hypophosphatasia. It was shown that genetically modified knock-out mice lacking the TNSALP gene had progressive osteopathy but no secondary hyperparathyroid disorder. The function of bone ALP in the mineralization process has not been clearly determined. It is assumed to elevate the local concentration of inorganic phosphate, locally inhibit mineralization or act as calcium-binding protein.

Patients with prostate, breast or lung carcinoma often develop skeletal metastases in the course of the disease. In this case, bone is resorbed by osteoclasts and newly formed by osteoblasts. Elevated bone ALP is only to be expected if the osteoblast activity is not lower than the osteoclast activity. Hence, elevated ALP is common in tumor diseases associated with osteoblastic metastasis, such as prostate carcinoma; in contrast, ALP levels in diseases associated with osteolytic metastasis are dependent on compensatory osteoblast activity. If bone metastasis is present, biphosphonates are used to inhibit bone resorption and reduce bone pain. The resulting increase in bone ALP about one month after start of therapy is thought to be caused by increased recruiting of osteoblasts. The decrease in bone ALP occurring after 2–3 months is thought to indicate the return to the coupling of bone resorption and bone formation.

It has been generally accepted that osteoporosis represents increased postmenopausal bone loss and is attributed to increased bone remodeling. The bone mass of women suffering from osteoporosis is negatively correlated with the biomarkers of bone formation and resorption. However, the predictive value of the individual bone marker is low. The combination of bone ALP, osteocalcin, N-terminal propeptide (PINP), carboxy-terminal cross-linked telopeptides and calcium excretion is thought to have a predictive value of 60–70%.

1.3.7.3 Intestinal ALP

The intestinal ALP is expressed by the enterocytes and can be easily measured in the blood of secretors of the H blood group substance (blood groups 0 and B). The proportion of intestinal ALP in total ALP in such individuals is about 10–20%. The activity of intestinal ALP increases after food intake, especially after high-fat meals.

The intestinal ALP can be elevated in patients with liver cirrhosis and other severe hepatopathies. The elevations are caused by an absolute reduction in asialoglycoprotein receptors. Intestinal ALP is bound to the surface of the hepatocyte membrane by these receptors and then disintegrated. Moreover, in autoimmune hepatitides, antibodies to the asialoglycoprotein receptor can occur and inhibit the receptor. Congestion in the small intestine in cases of right heart failure can induce increased synthesis of intestinal ALP.

1.3.7.4 Placental ALP

The placental ALP is a heat-stable fetal isoenzyme. There is homology with the Regan-type ALP. Placental ALP is produced by placental syncytiotrophoblast from fetal week 12 on and is present in serum as a tetramer with a molecular weight of 300 kDa. Significant amounts of Regan-type ALP are detected in seminomas and ovarian tumors. However, this enzyme is not specific to such tumors, but is also detected in the plasma membrane of type 1 pneumocytes and on the basal membrane between these cells. A high percentage of the Regan-type ALP, an isoenzyme usually not detectable in healthy individuals, can be measured in smokers. There is a linear relationship between nicotine intake and the level of Regan-type ALP. The concentration declines 1–2 months after smoking has been given up.

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71. Tenorio J, Alvarez I, Rianco-Zarrabeitia L, Martos-Moreno GA, Mandrile G, de la Flor Crespo M, et al. Molecular and clinical analysis of ALP in a cohort of patients with suspicion of hypophosphatasia. Am J Genet A 2017; 173: 601–10.

72. Adachi J. Corticosteroid-induced osteoporosis. Am J Med Sci 1997; 313: 41–9.

73. Dufour DR, Lott JA, Nolte FS, Gretch DR, Koff RS, Seeff LB. Diagnosis and monitoring of hepatic injury.I. Performance characteristics of laboratory tests. Clin Chem 2000; 46: 2027–49.

74. Tibi L, Collier A, Patrick AW, Clarke BF, Smith AF. Plasma alkaline phosphatase isoenzymes in diabetes mellitus. Clin Chim Acta 1988; 177: 147–56.

75. Salway JG. Drug test interactions handbook. London: Chapman and Hill, 1990.

76. Heins M, Heil W, Withold W. Storage of serum or whole blood samples? Effects of time and temperature on 22 serum analytes. Eur J Clin Chem Clin Biochem 1995; 33: 231–8.

77. Garnero P, Delmas PD. Assessment of the serum levels of bone alkaline phosphatase with a new immunometric assay in patients with metabolic bone disease. J Clin Endocrinol Metab 1993; 77: 1046–53.

78. Koshida K, Takahashi M, Kawana K, Inoue T. Comparison of markers for bone formation and resorption in premenopausal and postmenopausal subjects, and osteoporosis. J Clin Endocrinol Metab 1995; 80: 2447–50.

79. Coburn SP, Mahuren JD, Jain M, Zubovic I, Wortsman J. Alkaline phosphatase (EC 3.1.3.1) in serum is inhibited by physiological concentrations of inorganic phosphate. J Endocrinol Metab 1998; 83: 3951–7.

1.4 α-Amylase

Klaus Lorentz

Human α-amylases (1,4-α-D-glucan 4-glucanohydrolase, EC 3.2.1.1) are monomeric proteins with 97% homologous amino acid sequences in the pancreatic enzyme (P-amylase) and salivary gland enzyme (S-amylase). The isoenzymes from the pancreas and salivary gland have roughly the same catalytic activities in the serum and urine of healthy individuals. Lipase is another enzyme available for determination besides α-amylase in suspected acute pancreatitis and is given preference by many clinicians (see also Section 1.12 – Lipase).

1.4.1 Indication

1.4.2 Method of determination

Principle: The enzyme activity is measured continuously by the breakdown of defined oligosaccharides carrying an aromatic residue at the reducing group of the first glucose molecule (G1). Upon attack of 2-chloro-4-nitrophenyl-α-D-maltotrioside by α-amylase, the aromatic residue is directly liberated and measured. Using the IFCC method with a longer-chain substrate (EPS), the aromatic residue 4-nitro phenyl-G (7 – x) is dissociated by α-glucosidase and measured as yellow chromophore. Substitution at the carbon atom 6 of the glucose (G7) of the non-reducing end protects the oligosaccharides from attack by auxiliary enzymes.

Method of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) /1/

EPS + H 2 O α-amylase 4.6-ethylidene-G x + 4-nitrophenyl-G (7–x) 4-nitrophenyl-G (7–x) + (7–x) H 2 O α-glucosidase (7–x) glucose + 4-nitrophenoxide

Abbreviations: EPS, 4.6-ethylidene(G1)-4-nitrophenyl(G7)-α-(1–4)-maltoheptaoside; G, α-(1–4)-D-glucopyranosyl

1.4.3 Specimen

1.4.4 Reference interval

Refer to Tab. 1.4-1 – Reference intervals of amylase.

1.4.5 Clinical significance

1.4.5.1 α-Amylase in serum

An increase in enzyme activity in serum is the only uncontroversial diagnostic finding in the detection of pancreatic disease. In acute and recurrent inflammations, it is most reliably detected within the optimal diagnostic interval of 5–10 hours after the onset of pain in the upper abdomen. The quality of diagnostic information is defined by the upper reference limit besides the stage of the disease. Pancreatic amylase is considered superior to α-amylase (total) /6/, but the time of analysis is more important than the selection of the enzyme. α-Amylase and lipase regularly show parallel behavior with delayed decline of lipase to normal levels. The activities in serum in no way reflect the severity of the disease because α-amylase and lipase activities below 3 × the upper reference limit are also measured in severe courses /7/.

Levels within the reference interval (especially for α-amylase) occasionally occur in acute, preferably alcohol-induced, pancreatitis /7/. On the other hand, elevated α-amylase is observed in 8% of hospitalized patients without the presence of pancreatic disease. Hence, determination is not indicated if pancreatic disease is not suspected /8/.

Elevated levels indicate the following diseases:

Chronic asymptomatic hyperamylasemias are based on pancreatic or extra pancreatic diseases in about half of the cases; macroamylasemia and/or familial hyperamylasemia are diagnosed in about 5% of the cases, each, and no cause is found in 40% of the cases /14/. The existence of the ubiquitous isoform X-amylase is of intestinal origin, and P-amylase and S-amylase can originate from neoplasms and hepatic tissues /15/. Therefore, elevated α-amylase and lipase can be expected in liver diseases /16/, but also following cardiac circulatory failure with liver congestion /17/ that generally induces hyperamylasemia. Moreover, ascending parotitis should also be considered in postoperative stomatitis.

Elevated α-amylase and lipase by 10–15% have been described in fructose malabsorption /18/ and anticonvulsant therapy /19/. Pancreatic carcinomas cause hyperenzymemia in pancreatic duct occlusion. In bulimia and anorexia, amylasemias occasionally reach levels as high as 2 × the upper reference limit /20/, mostly due to parotitis following stomatitis. Other causes of extrapancreatic hyperamylasemias are shown in Tab. 1.4-3 – Causes of extra pancreatic hyperamylasemias.

Low levels in obese individuals have little significance. Hypoamylasemia as a symptom of pancreas failure or as missing response to a secretion stimulus (negative evocation test) is not found except in terminal stages.

1.4.5.2 α-Amylase in urine

A urine analysis is indicated in hyperamylasemia if macroamylasemia or renal insufficiency are suspected (see also Tab. 1.1-2 – Macroenzymes: characterization, clinical significance and laboratory findings).

1.4.5.3 α-Amylase in extravascular fluids

Postoperative analysis of drainage secretion is performed to determine the presence of a pancreatic fistula. High concentrations in pleural effusions (in basal pleuritis and thoracic duct injury) indicate pancreatitis. S-amylase is reported to be elevated in leukemias, lung carcinoma and lung metastasis /21/.

1.4.6 Comments and problems

Macroamylasemia (see also Section 1.1 – Diagnostic enzymology)

Macroamylases are non-uniform complexes (molecular weight above 400 kDa), in which α-amylase adheres to the Fab region of immunoglobulins (IgA in most cases, IgG under 30%, other Ig under 5%). In addition, albumin and α1-antitrypsin are found occasionally. Escaping glomerular filtration due to their size, they remain in the serum and cause up to 4-fold elevated activities. S-amylase is involved in most cases, but often not detected because the epitopes of the enzyme are covered by immunoglobulins. Characteristic findings include chronic hyperamylasemia without clinical correlate, normal or low amylase in urine and normal lipase activity. This harmless anomaly is found in 0.1% of the population. However, monoclonal gammopathies should be searched for in macroamylasemia.

Macro forms are more common following infusion of hydroxy ethyl starch (HAES) that forms high-molecular complexes with amylase. The supply of 500 mL 6% HAES causes elevated α-amylase concentrations for 3–5 days because glomerular filtration of the enzyme is only possible after HAES breakdown. This hyperamylasemia can be misdiagnosed as postoperative pancreatitis. The lipase level is normal.

Method of determination

All procedures measure up to 10 × the upper reference limit as a function of activity, and their substrates keep well in solution. Glucose concentrations above 10 g/L only slightly reduce the measured signal; pyruvate and lactate do not interfere.

Tests that release 4-nitro phenol or 2-chloro-4-nitro phenol as chromophore tolerate higher concentrations of bilirubin, triglycerides and hemoglobin, but the enzyme activity in samples with recent hemolysis (due to reduced hemoglobin absorption) is falsely indicated as too low /22/. Lipoproteins can cause low levels in lipemic sera.

Amylase in urine

The secretion and clearance of α-amylase allow certain diagnostic conclusions in suspected macroamylasemia and renal insufficiency, whereas determination in urine and the clearance ratio have no significance in the diagnosis of acute pancreatitis.

Anticoagulants

EDTA and oxalate are not recommended because of the binding of Ca2+, heparin does not interfere. Some tests include magnesium in the reagent to reactivate amylase in EDTA plasmas.

Reference interval

The α-amylase has a typical age profile with high individual fluctuations. Pregnancy has no effect. The concentration of salivary enzyme in neonates is only 25–50% of the final level reached after 12 months. Pancreatic amylase only appears after 1–2 months of life and increases continuously up to 10 years of age; after this, the reference interval for adults applies.

Stability

Stable in serum for 1 week at 4 °C or 25 °C or for at least 1 year at –28 °C (also for evidence of macroamylasemia). Unchanged activity for at least one day at 4 °C in urine and even up to one month in sterile storage; do not deep-freeze.

1.4.7 Pathophysiology

Human α-amylases [1,4-α-D-glucanglucanohydrolases, EC 3.2.1.1] represent three almost identical monomeric proteins. After dissociation of a signal peptide of 15 amino acids, they pass from the endoplasmic reticulum into the cytoplasm as active enzymes with uniformly 496 amino acids /23/. Their gene loci in the chromosome 1p21 encode as follows for three isoenzymes with molecular weights around 54 kDa: AMY2A for the pancreatic enzyme, AMY2B for the ubiquitous enzyme and AMY1 for the enzyme of the salivary glands. It has 97% homology with pancreatic amylase, with 15 deviating amino acids; the ubiquitous isoenzyme even has 98% homology due to only 5 substituted amino acids. Hence, salivary gland amylase can be inhibited to residual activity below 3% by concurrently using two monoclonal antibodies; however, this does not apply to the ubiquitous isoenzyme. There exist glycosylated forms of the two isoenzymes with a molecular weight of 57–62 kDa. Their glucan residues can be dissociated enzymatically in vivo with no loss of activity.

Amylases consist of three domains. Domain A includes the active center with activating Cl that can be substituted by anions of similar size. A protective Ca2+ in domain B aligns against the catalytic center and stabilizes the enzyme molecule, which therefore is inactivated by calcium-complexing anticoagulants and heavy metals. Domain C carries the glycan residue in glycosylated forms and varies strongly depending on the species. All isoenzymes reduce polymeric carbohydrates into disaccharides by random hydrolysis of 1,4-α-glucosidic bonds. Oligosaccharides are cleaved at preferred bonds which can result in glucose and maltose being transferred to the substrate.

α-Amylase is synthesized in the secretory epithelium of the salivary glands and pancreas and, in low concentration, also in hepatic and cancerous tissue /15/. As in lipase, a proenzyme can be detected in the acinus epithelium but does not appear extracellularly. In healthy individuals, more than 99% of the enzyme are released into the gastrointestinal tract, whereas impaired flow and inflammations of the organ/tissue result in increased amounts entering the circulation. Substantial destruction of secretory parenchyma has little effect on the activity in serum.

Otherwise, the enzyme behaves like lipase, but has a longer half-life (9.3–17.7 hours). Complete glomerular filtration and 50% tubular reabsorption of the α-amylase is thought to be the cause of this difference. Reabsorption is restricted due to tubular damage (in burns, ketoacidosis, acute pancreatitis) and proteinuria /24/, and amylase clearance (normally 2.8–4.6 mL/min.) increases as a result. This also increases the clearance ratio [(amylase clearance/creatinine clearance) × 100] from 1.8–3.2% in healthy individuals to more than 10%. Mostly glomerular damage (chronic glomerulonephritis, nephrosclerosis) slightly increases the ratio to as high as 9% due to a major decline in creatinine filtration. A relative increase in the pancreas fraction and a pronounced decrease in α-amylase excretion are observed.

References

1. Schumann G, Aoki R, Ferrero CA, Ehlers G, Ferard G, Gella FJ, et al. IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 370 C. Reference procedure for the measurement of catalytic concentration of α-amylase. Clin Chem Lab Med 2006; 44: 1146–55.

2. Lorentz K, Gütschow B, Renner F. Evaluation of a direct α-amylase assay using 2-chloro-4-nitrophenyl-α-D-maltotrioside. Clin Chem Lab Med 1999; 37: 1053–62.

3. Genzyme Diagnostics. Amylase dual reagent (instructions for use) 1994.

4. Junge W, Wortmann W, Wilke B, Waldenström J, Kurrle-Weittenhiller A, Finke J, Klein G. Development and evaluation of assays for the determination of total and pancreatic amylase at 37 °C according to the principle recommended by the IFCC. Clin Biochem 2001; 34: 607–15.

5. Abicht K, Heiduk M, Körn S, Klein G. Lipae, p-amylase, CRP-hs and creatinine: reference intervals from infancy to childhood. Abstract 15th IFCC-FESC, Barcelona 2003.

6. Melzi d’Eril GV, Bosoni T, Lesi C. Pancreatic amylase in serum for differential diagnosis of acute pancreatitis and acute abdominal diseases. Clin Chem 1989; 35: 2142–3.

7. Lankisch PG, Burchard-Reckert S, Lehnick D. Underestimation of acute pancreatitis: patients with only a small increase in amylase/lipase levels can also have or develop severe acute pancreatits. Gut 1999; 44: 542–4.

8. Lankisch PG, Doobe C, Finger T, Lübbers H, Mahlke R, Brinkmann G, et al. Hyperamylasemia and/or hyperlipasemia: incidence and underlying cause in hospitlized patients with non-pancreatic diseases. Scand J Gastroenterol 2009; 44: 237–41.

9. Gwozdz GP, Steinberg WM, Werner W, Henry JP, Pauley C. Comparative evaluation of the diagnosis of acute pancreatitis based on serum and urine assays. Clin Chim Acta 1990; 187: 243–54.

10. Dominguez-Muñoz JE, Pieramico O, Büchler M, Malfertheiner P. Ratios of different serum pancreatic enzymes in the diagnosis and staging of chronic pancreatitis. Digestion 1993; 54: 231–6.

11. Müller-Hansen J, Müller-Plathe O, Pröpper H. Untersuchungen zur diagnostischen Sensitivität von Lipase- und Amylase-Bestimmungen. Einfluß der ERCP auf die Aktivität von Serum-Lipase und Amylase. Ärztl Lab 1986; 32: 17–23.

12. Conn M, Goldenberg A, Concepcion L, Mandeli J. The effect of ERCP on circulating pancreatic enzymes and pancreatic protease inhibitors. Am J Gastroenterol 1991; 86: 1011–4.

13. Gottlieb K, Sherman S, Pezzi J, Esber E, Lehman GA. Early recognition of post-ERCP pancreatitis by clinical assessment and serum pancreatic enzymes. Am J Gastroenterol 1996; 91: 1553–7.

14. Pezzilli R, Morselli-Labate M, Casadei R, Campana D, Rega D, Santini D, et al. Chronic asymptomatic pancreatic heperenzymemia is a benign condition in only half of the cases: a prospective study. Scand J Gastroenterol 2009; 44: 888–93.

15. Nakamura Y, Tomita N, Nishide T, Emi M, Horii A, Ogawa M, Mori T, Kosaki G, Okabe T, Fujisawa M, Ohsawa N, Kameya T, Matsubara K. Production of salivary type α-amylase in human lung cancer. Gene 1989; 77: 107–12.

16. Tsuzuki T, Shimizu S, Takahashi S, Iio H. Hyperamylasemia after hepatic resection. Am J Gastroent 1993; 88: 734–6.

17. Góth L, Mészáros I, Scheller G. Hyperamylasemia and α-amylase isoenzymes in acute liver congestion due to cardiac circulatory failure. Clin Chem 1989; 35: 1793–4.

18. Ledochowski M, Murr C, Lass-Flörl C, Fuchs D. Increased serum amylase and lipase in fructose malabsorbers. Clin Chim Acta 2001; 311: 119–23.

19. Hermida J, Tutor JC. Serum amylase and lipase activities in epileptic patients treated with enzyme-inducing anticonvulsant drugs. Clin Chim Acta 2001; 303: 181–3.

20. Hempen I, Lehnert P, Fichter M, Teufel J. Hyperamylasämie bei Anorexia nervosa und bulimia nervosa. Dtsch Med Wschr 1989; 114: 1913–6.

21. Joseph J, Viney S, Beck P, Strange C, Sahn SA, Basran GS. A prospective study of amylase-rich pleural effusions with special reference to amylase isoenzyme analysis. Chest 1992; 102: 1455–9.

22. Gosling P, Zareian M. Fresh haemolysis interferes with blocked p-nitrophenyl-maltoheptaoside amylase methods. Ann Clin Biochem 1994; 31: 371–3.

23. Nishide T, Emi M, Nakamura Y, Matsubara K. Corrected sequences of cDNAs for human salivary and pancreatic α-amylases. Gene 1986; 50: 371–2.

24. Andreulli A, Bergia R, Masoero G, Biardi P, Pellegrino S, Tondolo M. Amylase to creatinine clearance ratio in renal diseases. Gastrenterology 1979; 77: 86–90.

1.5 Angiotensin-converting enzyme (ACE)

Lothar Thomas

Angiotensin-I-converting enzyme (peptidyl-dipeptidase A; EC 3.4.15.1) was originally described as dipeptidyl carboxypeptidase /1/. ACE is primarily localized in the endothelial cells of the pulmonary capillaries and the kidney cortex.

Tissue-specific ACE is involved physiologically (Fig. 1.5-1 – Biochemical effects of ACE):

Serum ACE (SACE) is not involved in these reactions; its pathophysiological significance remains to be clarified. Elevated SACE activities have been described for a number of diseases, especially sarcoidosis (Besnier-Boeck-Schaumann disease).

1.5.1 Indication

1.5.2 Method of determination

Routine assays cleave synthetic N-terminal blocked tripeptides, which release hippuric acid (benzoyl-glycine) upon splitting. Many synthetic substrates have been developed for ACE determination. The substrates are aryl-oligopeptides shorter than the natural substrates, usually tripeptides with blocked N-terminus, mainly hippuryl-glycyl-glycine (hippuryl as benzoylglycyl), hippuryl-histidyl-leucine (HHL) and furylacryloyl-phenylalanyl-glycyl-glycine (FAPGG). The substrates are used for the spectrophotometric, fluorimetric, radiometric and chromatographic methods /1/.

Method according to Lieberman /2/

Principle: the release rate of hippuric acid from HHL is measured by spectrophotometry at 228 nm after ethyl acetate extraction.

Method according to Neels et al. /3/

Principle: the release rate of glycyl-glycine from hippuryl-glycyl-glycine (hippuryl as benzoylglycyl) is determined in a chromogenic reaction. Photometric measurement at 420 nm.

Method according to Ryan et al. /4/

Principle: 3H-hippuryl-glycyl-glycine is used as a substrate and the release rate of 3H-hippuric acid is measured.

Method according to Friedland and Silverstein /5/

Principle: HHL is used as a substrate. The release rate of histidyl-leucine is determined spectrofluorimetrically after formation of a fluorescence adduct with orthophenylenediamine.

Method according to Holmquist et al. /6/

Principle: ACE catalyzes the hydrolysis of FAPGG to furylacryloyl-phenylalanine and glycyl-glycine. The hydrolysis causes a blue shift in the absorption of the assay medium. The reduction in absorption is measured at 340 nm. It is directly proportional to the ACE activity of the sample.

1.5.3 Specimen

Serum, heparin anticoagulated blood (no EDTA plasma): 1 mL

1.5.4 Reference interval

Refer to Tab. 1.5-1 – Angiotensin converting enzyme reference intervals.

1.5.5 Clinical significance

The serum ACE (SACE) activity in healthy individuals presumably involves released enzyme anchored as ectoenzyme in macrophages in the lumen-facing vessel wall /1/. Elevated SACE activities originate from granulomas. Granuloma is a feature of many chronic interstitial lung diseases such as sarcoidosis, hypersensitivity pneumonitis, berylliosis, histiocytosis X and are structured masses composed of activated macrophages and their derivatives, i.e. epithelioid cells and giant cells /8/. A few disease states, in addition to sarcoidosis, are consistently associated with elevated ACE in about 25% of the cases, for example Gaucher’s disease, hyperthyreosis, diabetes mellitus with retinopathy, liver cirrhosis, silicosis, asbestosis, lymphangiomyomatosis, chronic fatigue syndrome /9/.

Low ACE is thought to be a marker of endothelial dysfunction of the vascular bed, for example in pulmonary damage of toxic origin, deep vein thrombosis, hypothyroidism or after chemotherapy and radiotherapy of malignant tumors /1/. The validity of low SACE activities is unknown.

1.5.5.1 Sarcoidosis

Clinical aspects /810/

Sarcoidosis is a multi-systemic disease of unknown etiology. The typical findings are those with of non-caseating granulomas within the alveolar, bronchial and vascular walls. The disease predominantly occurs in young adults with an age peak of 30–40 years and affects the following organs:

The following forms of the disease are distinguished:

Prevalence: Germany 40–50/100,000 inhabitants, Spain, Italy < 10/100,000; there is a high prevalence in blacks and Puerto Ricans.

Prognosis

The natural course of sarcoidosis is not predictable. Patients with advanced pulmonary infiltrates and splenomegaly can have spontaneous remission, while others with asymptomatic hilar adenopathy can develop a severe clinical picture. Spontaneous remission occurs in 70% of patients with bi-hilar lymphadenopathy (type I), in 50% of patients with pulmonary infiltrates and bi-hilar lymphadenopathy (type II) and in 50% of patients with pulmonary infiltrates without bi-hilar lymphadenopathy (type III). Mortality is 40% in those with pulmonary fibrosis (type IV). Generally, the more severe the clinical findings at the time of diagnosis and the more organ systems are involved by the disease, the more frequent adverse courses are observed /8/.

Neurosarcoidosis /1112/

Neurological symptoms due to involvement of the central nervous system (CNS) occur in about 5% of patients with systemic sarcoidosis, 10–30% of the patients show initial neurological symptoms when presenting for the first time; the incidence of isolated CNS sarcoidosis is reported to be below 0.2 related to 100,000 Caucasians. Neurosarcoidosis can affect the meninges, brain parenchyma, spinal chord and peripheral nerves. The differentiation between intracranial sarcoidosis and other neurological disorders can be difficult, especially if there are no symptoms of extra cranial manifestation.

SACE in sarcoidosis

The ACE in serum is a useful test for:

Diagnostics: In acute pulmonary sarcoidosis, the positive predictive value of SACE is 75–90% and the negative is 70–80% /13/. The diagnostic sensitivity of elevated SACE activity in combination with a radiographic finding of type II or type II in the 67Ga scan is reported to be 100%. A normal SACE in combination with a negative 67Ga scan excludes pulmonary sarcoidosis. Chronic sarcoidosis is often associated with normal SACE levels; elevated activities also occur in other granulomatous diseases.

A normal SACE does not rule out sarcoidosis. This is because the SACE reference interval is dependent on the genetic polymorphism, and the reference values were defined without taking the polymorphism into account /14/. For example, acute sarcoidosis associated with erythema nodosum can show values within the reference interval /13/. In sarcoidosis of the liver manifested as sclerosing cholangitis, extrahepatic cholestasis or Budd-Chiari syndrome, the SACE is elevated in about 15% of the cases, and the ALP is always 2–5-fold elevated /15/.

Estimation of the granuloma load /13/: The ACE level reflects the granuloma load of the entire organism, independently of the affected organ. This especially applies to systemic sarcoidosis. Isolated sarcoidosis, for example sarcoidosis of the CNS or cardiac sarcoidosis, does not cause elevated ACE. This can also be the case in less vascularized, sometimes large mediastinal lymphomas.

Course of disease /13/: Initially low SACE activity is indicative of a good prognosis; the prognosis is less favorable if the activity is 2–3-fold elevated. The SACE activity increases along with the progression of the disease and reaches peak levels in chronic active disease with a high granuloma load.

Course under corticosteroid treatment /16/: The SACE level is generally not the criterion for a decision in favor of this treatment, but pronouncedly elevated activities above the upper reference limit can be considered an indication of need for treatment and good responsiveness. The higher the initial level, the longer the corticosteroid treatment must be to attain normal SACE levels and improvement of the clinical symptoms. An effective dosage usually results in decreasing SACE levels already after 1–2 weeks. In sarcoidosis of the lungs, the decrease precedes radiological improvement. The absence of a decrease is indicative of inadequate dosage or lack of compliance.

The SACE can increase again after the end of treatment and normalization of the SACE. This is the earliest sign of recurrence where clinical symptoms do not necessarily have to be present. Resumption of treatment is only indicated if clinical and radiological changes are detected.

Some cured patients can show SACE re-elevation without clinical recurrence. In this case, however, the enzyme activities are usually lower than the levels before start of treatment.

Spontaneous remissions of sarcoidosis are associated with a gradual decrease in SACE. The level does not decline as abruptly as under corticosteroid treatment.

ACE in neurosarcoidosis

Elevated activities of SACE and ACE in cerebrospinal fluid (CSF) are not specific of neurosarcoidosis and can also be measured in other neurological diseases such as CNS infections, brain tumors and Guillain-Barré syndrome /11/. Elevated ACE in CSF are detected in 55% of neurosarcoidosis cases, 5% of sarcoidosis cases without CNS involvement and 13% in other neurological diseases /17/. Other authors only see a significance of the ACE in CSF in the assessment of neurosarcoidosis under corticosteroid treatment /18/.

Other biomarkers in sarcoidosis /8/

1.5.5.2 Elevated SACE in other diseases

The determination of the SACE activity in the diseases listed in Tab. 1.5-2 – Elevated ACE at other diseases and conditions is only significant for the differential diagnosis because these diseases reduce the diagnostic specificity of SACE for the verification of sarcoidosis.

1.5.6 Comments and problems

Sampling

Serum or heparin anticoagulated blood should be used as specimen. Metal chelators such as EDTA are not suited as anticoagulant because they reduce the SACE activity. ACE is a metallopeptidase with a zinc atom in the active center; the binding of the zinc atom by the chelate former significantly reduces the enzyme activity.

ACE inhibitors such as captopril, enalapril must have been discontinued 4 weeks beforehand because otherwise the measured values are too low due to ACE inhibition /23/.

Method of determination

About 25% of the sera of patients, especially of sarcoidosis patients, contain an internal ACE inhibitor that significantly lowers the ACE activity. The inhibitory effect is mediated if the serum is diluted 1 : 10 /23/.

Tests using hippuryl-glycyl-glycine as a substrate are more suited than those using HHL because they are less susceptible to hydrolysis by carboxypeptidases /13/. Tests using FAPGG as a substrate have advantages because the hydrolysis rate is greater by a factor of 3. The reference interval is also higher as a result. Moreover, kinetic measurement is possible at 340–345 nm. Thus, measurements can be performed on mechanized automatic analyzers /7/. The effect of both substrates (HHL and FAPGG) is dependent on Cl. Therefore, the assay medium must have an NaCl concentration of 250–350 mmol/L /1/.

Reference interval

The intraindividual variation of SACE is small, while the inter individual variation is high. The factor 6, for example, ranges between the lower and upper reference limits in adults. Infants and boys in puberty have higher SACE activities than adults.

The following reference intervals have been determined for children based on the substrate FAPPG /24/:

0.5–2 yrs

109 ± 33

2–4 yrs

100 ± 30

4–9 yrs

124 ± 42

9–13 yrs

138 ± 47

13–18 yrs

126 ± 34 (boys)

102 ± 30 (girls)

Adults

100 ± 35

Values expressed as x ± s and in U/L.

Drugs /23/

Captopril inhibits the ACE activity at a half-life of 1–4 days in some patients and 10–17 days in others. The effect of captopril on the SACE activity can vary:

Enalapril inhibits the SACE activity almost completely; the effect cannot be reversed through storage, serum dilution or dialysis. Therefore, the administration of enalapril should be considered if the SACE levels are very low.

Stability

ACE is stable in serum and plasma for at least 1 week at +4 °C and for 3 months at –20 °C /7/.

1.5.7 Pathophysiology

ACE is an ubiquitous enzyme expressed by vascular endothelial cells, macrophages, proximal tubule kidney cells, Leydig cells and chorioid plexus cells. Therefore, it is present in many organs and especially abundant in the lungs and kidneys. It is an ectoenzyme bound to the outside of the cell membrane through a hydrophobic peptide residue. The SACE activity is released by enzymatic cleavage, especially from vascular endothelium of the lungs /1/.

ACE is a zinc metalloprotease with a molecular weight of 150–170 kDa. The difference in molecular weight is based on different glycosylation in the individual tissue; for example, the carbohydrate portion of ACE of the lung is 30% and contains fucose, mannose, N-acetylglucosamin, glucose and sialic acid /25/. ACE cleaves the last two amino acids of peptide substrates; each peptide serves as a substrate provided that proline is not the last but one amino acid.

ACE is a key enzyme of the renin-angiotensin system (RAS) and kallikrein system due to the following reactions:

Based on these reactions, the ACE has the following effects:

The dual role of ACE in blood pressure maintenance (Fig. 1.5-2 – Effect of ACE on the renin-angiotensin system (RAS) and kinin-kallikrein system) and homeostasis of the electrolyte and water balance have made it an ideal working point for medical treatment (ACE inhibitors) of high blood pressure and congestive heart failure.

Various polymorphisms of the ACE gene and possible disease associations have been identified /26/. They refer to both the ACE activity of the tissues and to SACE. The polymorphisms consist of the presence (insertion allele I) or absence (deletion allele D) of a 287 bp DNA fragment in an ALU repetitive sequence in intron 16 of the ACE gene /1/. The genotypes II, ID and DD are distinguished. The SACE activity in individuals of genotype DD is about twice as high as that in individuals of genotype II. However, there are no differences in ACE kinetics, in angiotensin II and aldosterone levels, and no significant differences in the blood pressure.

Sarcoidosis is a granulomatous disease of unknown genesis, characterized by an accumulation of activated T-cells and macrophages in the affected organ (the lungs in most cases). These release interferon-γ, TNF-α and other pro inflammatory cytokines as mediators of an inflammation and cellular immune reaction, causing the subsequent formation of non-caseating epithelioid cell granulomas. In the inflamed regions, there is a high number of CD4+T-cells. The inflammatory process is the same in all organs affected, including the CNS. The persistence of the inflammation induces fibrotic changes with irreversible tissue damage.

The sarcoid granulomas consist of lymphocytes, macrophages, epithelioid cells, mast cells, eosinophil granulocytes and fibroblasts. There is a strong influx of immune cells and a strong proliferation and apoptosis of cells in the granuloma. ACE is released during the conversion of macrophages in epithelioid cells. Alveolar macrophages stimulated by T-lymphocytes also release ACE into the circulation. Therefore, the SACE activity is an indicator of the organism’s granuloma load, while the concentration of sIL-2R, neopterin and sTNF-R II indicates the extent of immune cell activation in sarcoidosis /813/.

References

1. Baudin B. New aspects of angiotensin-converting enzyme: from gene to disease. Clin Chem Lab Med 2002; 40: 256–65.

2. Lieberman J. Elevation of serum angiotensin converting enzyme (ACE) level in sarcoidosis. Am J Med 1975; 59: 36–72.

3. Neels HM, van Sande ME, Sharpé SL. Sensitive colorimetric assay for angiotensin converting enzyme in serum. Clin Chem 1983; 29: 1399–403.

4. Ryan J W, Chung A, Ammons C, Carlton ML. A simple radioassay for angiotensin-converting enzyme. Biochem J 1977; 167: 501–5.

5. Friedland J, Silverstein E. A sensitive fluorometric assay for serum angiotensin-converting enzyme. Am J Clin Pathol 1976; 60: 416–20.

6. Holmquist B, Bunning B, Riordan JF. A continuous spectrophotometric assay for angiotensin-converting enzyme. Anal Biochem 1979; 95: 540–3.

7. Bénéteau B, Baudin B, Morgant G, Giboudeau J, Baumann F CH. Automated kinetic assay of angiotensin converting enzyme in serum. Clin Chem 1986; 32: 884–6.

8. Müller-Quernheim J. Sarcoidosis: clinical manifestations, staging and therapy (part II). Respiratory Medicine 1998; 92: 140–9.

9. Lieberman J. Angiotensin-converting enzyme in nonpulmonary sarcoidosis. Sem Resp Med 1992, 13: 399–401.

10. Schmidt M. Sarkoidose. Allergologie 1996; 19: 212–5.

11. Nowak DA, Widenka DC. Neurosarcoidosis: a review of its intracranial manifestation. J Neurol 2001; 248: 363–72.

12. Gullapalli D, Phillips LH. Neurologic manifestations of sarcoidosis. Neurologic Clinics 2002; 20: 59–81.

13. Bénéteau-Burnat B, Baudin B. Angiotensin-converting enzyme: clinical applications and laboratory investigations on serum and other biological fluids. CRC Rev Clin Lab Sci 1991; 28: 337–56.

14. Muller BR. Analysis of serum angiotensin-converting enzyme. Ann Clin Biochem 2002; 39: 456–43.

15. Blich M, Edoute Y. Clinical manifestation of sarcoid liver disease. J Gastroenterol Hepatol 2004; 19: 732–7.

16. Wurm K. Die Bedeutung des ACE-Tests bei Sarkoidose. Z Allgemeinmed 1987; 63: 1004–6.

17. Oksanen V. New cerebrospinal fluid, neurophysiological and neuroradiological examinations in the follow-up of neurosarcoidosis. Sarcoidosis 1987; 4: 105–10.

18. Dale JC, O’Brien JF. Determination of angiotensin-converting enzyme levels in cerebrospinal fluid is not a useful test for the diagnosis of neurosarcoidosis. Mayo Clin Proc 1999; 74: 535–9.

19. Rothkranz-Kos S, v Dieijen-Visser MP, Mulder PGH, Drent M. Potential usefulness of inflammatory markers to monitor respiratoy functional impairement in sarcoidosis. Clin Chem 2003; 49: 1510–7.

20. Feman SS, Mericle RA, Reed GW, May JM, Workman RJ. Serum angiotensin-converting enzyme in diabetic patients. Am J Med Sci 1993; 305: 280–4.

21. Ozawa T, Ninomiya J, Honma T, et al. Increased serum angiotensin-converting enzyme activity in patients with mixed connective tissue disease and pulmonary hypertension. Scand J Rheumatol 1995; 24: 38–43.

22. Quellete DR, Kelly JW, Anders GT. Serum angiotensin-converting enzyme level is elevated in patients with human immunodeficiency virus infection. Arch Intern Med 1992; 152: 321–4.

23. Lieberman J, Zakria F. Effect of captopril and enalapril medication on the serum ACE test for sarcoidosis. Sarcoidosis 1989; 6: 118–23.

24. Bénéteau-Burnat B, Baudin B, Morgant G, Baumann F Ch, Giboudeau J. Serum angiotensin converting enzyme in healthy and sarcoidotic children: comparison with the reference range for adults. Clin Chem 1990; 36: 344–6.

25. Das M, Soffer RL. Pulmonary angiotensin-converting enzyme: structural and catalytic properties. J Biol Chem 1975; 250: 6762–8.

26. Crisan D, Carr J. Angiotensin I-converting enzyme. Genotype and disease associations. J Molecular Diagn 2000; 2: 105–15.

1.6 Alanine aminotransferase (ALT), Aspartate aminotransferase (AST)

Lothar Thomas

The aminotransferases, also referred to as transaminases, are a group of enzymes catalyzing a reversible conversion of α-keto acids into amino acids by transferring an amino group. The ALT is located in the cytosol of the cells and can be found mainly in the liver and kidneys and, to a small extent, also in the myocardium and skeletal muscle. The main concentration of ALT occurs in the liver; hence, elevated activity in serum is a specific marker of liver disease. The AST is located in the cytosol and in the mitochondria of the cells. This ubiquitous enzyme is found in high concentrations in liver, nervous tissue, skeletal and cardiac muscle.

1.6.1 Indication

ALT

Serves as key parameter of hepatocellular injury and in monitoring and therapy assessment:

AST

Supplements the ALT in the diagnosis of liver disease:

1.6.2 Method of determination /12/

AST (EC 2.6.1.1)

IFCC Primary Reference Procedure for the Measurement of Catalytic Activity Concentration of Aspartate Aminotransferase at 37 °C

Principle: AST catalyzes the reaction between L-aspartate and 2-oxoglutarate and oxaloacetate formed is reduced by NADH catalyzed by malate dehydrogenase (MDH) (Fig. 1.6-1 – Principle of AST and ALT determination according to IFCC). Pyridoxal phosphate is added to activate apo-AST which may be present in the specimen. LD is added to reduce pyruvate and shorten the duration of preincubation needed in order to obtain a stable initial absorbance. The measured rate of NADH2 decrease is proportional to the AST activity.

ALT (EC 2.6.1.2)

IFCC Primary Reference Procedure for the Measurement of Catalytic Activity Concentration of Alanine Aminotransferase at 37 °C

Principle: ALT catalyzes the reaction between L-alanine and 2-oxoglutarate, and the pyruvate formed is reduced by NADH in a reaction catalyzed by LD (Fig. 1.6-1 – Principle of AST and ALT determination according to IFCC). Pyridoxal phosphate is added to activate apo-ALT which may be present in the specimen. The measured rate of NADH2 decrease is proportional to the ALT activity.

1.6.3 Specimen

Serum, plasma (heparin, EDTA, citrate, oxalate): 1 mL

1.6.4 Reference interval

See Tab. 1.6-1 – Reference interval

1.6.5 Clinical significance

Elevated aminotransferases indicate the presence of liver disease; normal levels, however, do not exclude such a disease, especially in chronic hepatitis. In the USA, the prevalence of elevated aminotransferase levels is 7.9% and correlated to fatty liver disease. Aminotransferases are also a predictor of the metabolic syndrome (MetS), diabetes mellitus (DM) and cardiovascular disease. According to the Framingham Offspring Heart Study /6/, among individuals at baseline, per 1 standard deviation increase in log ALT level, there were increased odds of the development of MetS [odds ratio (OR) 1,21] and DM (OR, 1.48) over 20 years of follow-up.

In pediatric hospitals /7/, about 12% of isolated aminotransferase elevations are due to genetic disorders. In particular cases of muscular dystrophy masquerading as liver disease and false diagnosis of cryptogenic liver disease in patients with cystic fibrosis, celiac disease, glycogen storage disease and other congenital metabolic disorders.

The AST is no longer significant in the diagnostics of acute myocardial infarction (AMI) and much less sensitive in the diagnostics of skeletal muscle diseases than the CK. Therefore, the AST in AMI and myopathies is only analyzed for differential diagnostic reasons.

1.6.5.1 Liver diseases

The ALT is a key biomarker for the inflammatory damage of the liver parenchyma. It is the basic marker in laboratory staging of liver disease and requested in the following cases:

The frequency (%) of elevated ALT levels in liver disease is shown in Tab. 1.6-2 – ALT activities in serum and their frequency in hepatobiliary diseases. The increase of ALT and AST in hepatopathies is assessed in Tab. 1.6-3 – Aminotransferases in patients with hepatopathies.

1.6.5.1.1 Screening for liver disease

The aminotransferases, GGT, ALP and CHE are recommended as screening pattern for liver disease. For this purpose, elevated aminotransferase levels serve as a biomarker of parenchymal injury, elevated GGT serves as an indicator of metabolic toxic damage, the ALP serves as a biomarker of cholestasis, and decreased CHE serves as an indicator of reduced functional hepatocyte mass. Up to 90% of patients with liver injury are diagnosed based on this enzyme pattern. The laboratory findings do not indicate functional hyperbilirubinemias, cases with non-alcoholic fatty liver disease, chronic hepatitis C and residual stages of hepatitides without inflammatory activity of the liver parenchyma. In a study /8/ on 1,154 patients with hepatobiliary diseases, 15% did not show elevated ALT. The majority of the patients suffered from liver metastases, extrahepatic bile duct obstruction, liver cirrhosis and drug-induced liver injury. The cirrhosis patients showed lower CHE levels, the others mainly elevated GGT levels. Since there is no indication of increased ALT production in the hepatocytes in liver injury, any level exceeding the upper reference limit is primarily considered an indication of liver injury. Unexpected elevations of ALT or AST should be verified by determination using a new sample. This is because the intraindividual variation of the aminotransferases is 10–30% from one day to the next; moreover, elevated activities can also be measured after heavy physical exertion.

1.6.5.1.2 Medical decision-making approach in symptomatic patients

Acute abdominal pain: The enzyme pattern should be selected such as to allow the detection of other diseases such as pancreatitis, ileus, tubal pregnancy or myocardial infarction besides acute liver injury due to acute hepatitis, acute bile duct obstruction, acute cholecystitis and acute impaired perfusion disorder. Therefore, besides ALT, AST and GGT, the diagnostic pattern should include GLD, lipase or α-amylase, cardiac troponin and hCG as well as the blood count and C-reactive protein as supplementary parameters. ALT levels within the reference interval exclude acute liver disease or liver involvement. This also applies to acute obstructive jaundice, which can also be ruled out if the ALT level is more than 20-fold the upper reference limit. In acute alcoholic hepatitis, one of the few acute liver diseases besides the Reye syndrome where the AST is initially higher than the ALT level, the aminotransferase activities are 10–20-fold the upper reference limit.

If the aminotransferases are elevated more than 20-fold the upper reference limit, differential diagnosis has to decide between acute viral hepatitis, acute impaired perfusion and acute toxic liver injury. The GLD is about as high as the aminotransferase levels in impaired perfusion, about half as high in toxic injury and not higher than 10% of the aminotransferase activity in viral hepatitis. The determination of the CHE allows to differentiate between acute intoxication and acute impaired perfusion. Whereas the CHE level decreases to below 50% of the lower reference limit in intoxication, this does not apply to impaired perfusion /7/.

Jaundice and sub jaundice: In icteric patients or in the presence of hyperbilirubinemia, a differentiation between hepatic and hemolytic jaundice is required. The LD/AST ratio is significant besides the determination of the total and direct-reacting bilirubin; a ratio > 5 indicates the hemolytic genesis of jaundice (see also Section 1.11 – Lactate dehydrogenase (LD) and Section 5.2).

Coma: In a comatose condition, it is important to recognize the hepatic coma. In the setting of hepatogenic coma, a differentiation must be made between fulminant liver failure and hepatic encephalopathy. The aminotransferase levels in hepatic encephalopathy are similar to those of liver cirrhosis, i.e., they are mildly to moderately elevated, while those in fulminant liver failure due, for example, to paracetamol or death cap poisoning, or in halothane-induced cases show a characteristic necrosis pattern. The ALT and AST are more than 20-fold elevated, with the AST being higher than the ALT, and the GLD is on a similar level. In most cases of portosystemic encephalopathy, the CHE level is already low on admission of the patient, whereas in fulminant liver failure, the CHE decreases together with the albumin after the coagulation factors due to its long half-life.

Distinction and differentiation of cholestasis: The screening pattern by itself already indicates the presence of cholestasis. High GGT and ALP at only mildly to moderately elevated ALT levels indicate cholestasis, while much higher ALT levels compared to the GGT and ALP indicate hepatitis. A differentiation based on laboratory findings as to whether the cholestasis involves the large bile ducts, i.e., is of extrahepatic origin, or whether an intrahepatic obstruction of the small bile ducts and/or toxic accompanying cholestasis is present, can only be performed after extrahepatic cholestasis has been excluded by imaging.

1.6.5.1.3 Severity assessment of liver disease

The activity of the aminotransferases in serum is both correlated with the amount of damaged hepatocytes and the severity of the single cell damage and thus the acuteness of the liver disease. The damage of about 1 in 750 hepatocytes induces elevated ALT levels to beyond the upper reference limit. Information regarding the severity of cell damage is provided by the AST/ALT ratio (De-Ritis ratio). About 70% of the AST activity of the hepatocyte is located in the mitochondria and 30% is located in the cytoplasm. Ratios below 1.0 indicate a milder degree of liver injury, especially involving acute, reversible, inflammatory liver diseases such as acute viral hepatitis B. Ratios > 1.0 indicate a high degree of liver injury of the necrosis type /10/.

Acute hepatocellular injury: Acute liver disease can be due to viral hepatitis, alcoholic hepatitis, bile duct obstruction, toxic damage or acute impaired perfusion. Elevated ALT or AST levels higher than 10-fold the upper reference limit almost always indicate the presence of these diseases.

Chronic hepatocellular injury /10/: Chronic liver disease is defined as continuous hepatocellular necrosis and inflammation of the liver, in many cases associated with fibrosis. Chronic liver disease can proceed into liver cirrhosis and is the precondition for the development of hepatocellular carcinoma. In many cases, it results from hepatotropic viral infections, causes minimal symptoms and entails the risk of increased morbidity and mortality in the longer term. The persistence of ALT for more than 6 months after acute hepatitis B or elevated ALT levels measured several times within 6 months without a plausible explanation indicate chronic liver disease.

There is a correlation between progression and aminotransferase activity in chronic liver disease. Activities are high if cirrhosis develops quickly. In chronic liver disease, the ALT is usually higher than the AST level, or the AST is even normal. With advancing reduction of the liver parenchyma, the ALT deceases more strongly than the AST level and the De-Ritis ratio reaches values above 1. Chronic alcoholic hepatitis is an exception. Here, the De-Ritis ratio is above 1 (often even above 2) already from the very beginning. Drugs and chronic alcohol consumption are the essential causes of chronic liver disease in patients with negative virus markers. Other liver diseases associated with elevated ALT should not be forgotten, for example autoimmune hepatitis, cholestatic liver disease, α1-antitrypsin deficiency and Wilson’s disease.

Liver cirrhosis /10/: Liver cirrhosis is characterized by fibrosis and the transformation of normal hepatic structure into abnormal lesions. It results from chronic liver disease with progressive necrosis of liver parenchyma. The developing regenerative nodules are not a fully adequate replacement for the necrotized parenchyma. This results in restricted liver function based on a reduced metabolic rate and reduced presence of enzymes in the hepatocytes. The advancing reduction of intact liver parenchyma is reflected by mildly elevated ALT and AST levels and an increased De-Ritis ratio. For the recognition of liver cirrhosis, the diagnostic sensitivity of a ratio > 1 is 32–83% and the diagnostic specificity is 75–100% /1112/.

The increasing reduction in liver function is indicated by the change in biomarkers. An extension of the prothrombin time, decreasing CHE, albumin and thrombocyte count are important indications of progression. These parameters should be determined every 3–6 months in liver cirrhosis monitoring.

1.6.5.1.4 Liver disease staging

The stage of acute liver disease can be assessed based on the changes of the aminotransferases over time and the correlation with the bilirubin concentration. The AST/ALT ratio, which decreases during curing, allows to assess the stage of the disease because the half-life of ALT (47 hours) is about three times as long as that of AST (17 hours). For example, the ratio is 0.6–0.8 in acute hepatitis as the ALT and AST reach peak levels, then decreases gradually and is 0.2–0.4 in the fourth week of the disease. The LD can be helpful in differentiating remittent icteric hepatitis from the early form of mild acute hepatitis with a low AST/ALT ratio. Whereas the LD activity is already normal again in the remittent form of the disease due to its half-life of only 10 hours, it ranges between the AST and ALT levels in the acute mild form /6/.

Aminotransferases in relation to bilirubin /10/: In acute viral hepatitis B, ALT and AST show peak levels at the onset of jaundice in the first week of the disease. The bilirubin reaches peak levels up to one week later. The aminotransferases decline continuously by about 10% each day at the onset of jaundice. The ALT remains elevated for 27 ± 16 days and the AST remains elevated for 22 ± 16 days. In acute toxic hepatitis and acute impaired liver perfusion, the peak levels of the aminotransferases are already reached within 24 hours after admission to hospital, where the AST is higher than the ALT. The aminotransferase levels decline again within the next 24 hours. The AST can decline by up to 50% and – due to its short half-life – decreases more pronouncedly than the ALT. The AST can return to within the reference interval already 7 days after acute injury.

1.6.5.1.5 Etiological verification of liver disease /911/

The etiological verification of liver disease is part of the differential diagnosis and a prerequisite for causal therapy. The diagnostic value of the aminotransferases is small in this context. This especially applies to liver disease with mild injury-induced or approximately identical enzyme changes that occur, for example, in acute and chronic viral hepatitides and liver cirrhosis. Moreover, chronic active hepatitides caused by hepatotropic viruses can lead to enzyme changes to a similar degree as can acute hepatitides caused by non-hepatotropic viruses. Drug-induced toxic liver injury manifested as hepatitic or cholestatic forms, fatty liver or variable combinations can also be a problem.

The following assays are useful for etiological verification and ensure pathogenic evidence quality (see also Section 1.2 – Biomarkers of liver disease):

Etiological verification is possible to some extent in chronic hepatitis and liver cirrhosis by diagnostic enzymology in combination with serum protein electrophoresis and/or immunoglobulin determination. For example, autoimmune liver diseases and cirrhoses can be associated with hyperproteinemia and/or a high γ-globulin fraction in serum protein electrophoresis or – due to IgA increase – show a blended β- and γ-globulin fraction in alcohol-toxic etiology. Posthepatitic cirrhosis shows increased concentration of IgG, and primary biliary cirrhosis shows increased concentration of IgM relative to the other immunoglobulin classes.

1.6.5.1.6 Prognostic assessment of hepatitis

Prognostic assessment is focused on the following questions /8/:

Cured hepatitis: Acute viral hepatitis A and B are usually self-limiting; almost all cases of hepatitis A and 95% of the cases of hepatitis B are cured. About 85% of acute hepatitis C infections proceed into a chronic form. During the acute phase of hepatitis, the aminotransferases do not allow any conclusion as to whether hepatitis will be cured or develop into a chronic form in individual cases. The ALT and GGT are the last enzymes to return to normal levels. Therefore, monitoring is recommended including measurements every 2 weeks. If the enzyme levels have not normalized within 6 months or show recurrent elevations, a chronic form must be expected. This always applies if no antibodies against HBsAg and HBeAg are produced or if virus persistence is detected.

Transition into severe form: Enzyme analyses should detect patients with increased risk of liver failure. This applies to the necrotizing forms and affects 0.1% in hepatitis A and C, about 1% in hepatitis B, up to 20% in hepatitis D and up to 4% in hepatitis E (up to 20% in pregnant women). The level of aminotransferases is rather based on the etiology of acute liver injury than on severity. Therefore, the absolute level of aminotransferase activity cannot be used for prognostic assessment. However, a poor prognosis suggests itself if the necrosis pattern consists of decreasing levels of all hepatocyte enzymes or decreasing ALT and concurrently elevated AST, GLD and LD levels.

Antiviral hepatitis treatment /1314/: In virustatic treatment of chronic hepatitis B and C, the ALT is determined to assess treatment success. This is because the ALT is a biomarker for assessing the inflammatory activity of the liver, although it only allows limited conclusions regarding the extent of the inflammation and provides little information on the severity of fibrosis. For further information, see Section 1.2 – Biomarkers of liver disease.

1.6.5.2 Myopathies

The diagnostic sensitivity of the AST in acute myocardial infarction is 96% and the diagnostic specificity is 86% 12 hours after the acute event /15/. The ALT is only significant in the course of infarction if right heart failure is suspected. The sensitivity and specificity of the AST are less informative for the diagnosis of skeletal muscle diseases than those of the CK. Elevated AST and CK levels are indicative of muscle damage.

The levels of AST and ALT in myocardial disease are shown in Tab. 1.6-4 – Aminotransferases in cardiac diseases and diseases with similar symptoms and in disease of the skeletal muscle disease in Tab. 1.6-5 – Aminotransferase behavior in skeletal muscle damage.

1.6.6 Comments and problems

Method of determination

The IFCC method is optimized for 37 °C and contains pyridoxal-phosphate in the reagent mixture. Before the specific reaction is started by adding α-ketoglutarate, the ALT and/or AST are activated by saturation with pyridoxal-phosphate in a preincubation step. In addition, in the presence of NADH, pyruvate in the sample is converted to lactate /12/. The addition of pyridoxal-phosphate has the advantage of stabilizing the enzymatic activity of the aminotransferases. Without the addition of pyridoxal-phosphate, falsely low activities are measured in samples with an insufficient concentration of endogenous pyridoxal-phosphate, for example in patients with myocardial infarction, liver disease or in intensive care patients.

A reduction in NADH would occur in the AST assay medium without the removal of pyruvate in the preincubation step /16/.

The ALT level and the upper reference limit are dependent on the analyzer. In a statewide study, for example, the inter laboratory variations were 69–83 U/L (variation of 14 U/L), but only 4–8 U/L if the measurements in the different laboratories were performed with an analyzer of the same diagnostics manufacturers /17/.

Specimen

Serum is recommended; heparin anticoagulated blood can cause turbidity of the assay medium /1/.

Reference interval

The upper reference levels (URLs) are optimized for the IFCC method and refer to adults at 20–60 years of age /12/. The levels of Americans of African origin are 15% higher than those of Caucasians. In adults, the American College of Gastroenterology recommends ALT URLs of 33 U/L for males and 25 U/L for females, respectively. In Children the North American Society of Pediatric Gastroenterology, Hepatology and Nutrition states gender-specific URLs (26 U/L for boys and 22 U/L for girls). As a result of the inappropriate application of these URLs, there is a potential for over diagnosis /18/.

Macro AST

See Tab. 1.1-2 – Macroenzymes: characterization, clinical significance and laboratory findings.

Hemolysis

At ALT levels within the reference interval and a Hb value of 2.5 g/L and higher, hemolysis causes an elevation of the ALT by about 10%. The AST increases with increasing hemolysis starting from Hb values of 1.5 g/L. The activity of the ALT in the erythrocytes is 7-fold and that of the AST is 15-fold higher than in serum /19/. Hemolytic anemias cause mildly elevated AST levels at pronouncedly elevated LD; potassium is normal in in-vivo hemolysis and elevated in in-vitro hemolysis.

Biological factors

Half-life (hours) /20/: AST 17 ± 5, mitochondrial AST 87, ALT 47 ± 10.

Variation: The variation of aminotransferase levels in serum within day is 45%, with highest levels reached in the evening and lowest at night. Day-to-day variation is 5–10% /20/.

Body weight: The aminotransferase level in individuals with a high body mass index is 40% higher than in normal-weight individuals /20/.

Hemodialysis patients: Such patients may have low AST and ALT due to pyridoxal-phosphate deficiency /16/.

Stability

In serum ALT and AST are stable for 1 week at 9 °C; the AST decreases slightly continuously at 20 °C /21/.

1.6.7 Pathophysiology /6789/

The increase in serum activity of usually structure-committed liver enzymes is an indicator for architectural and functional disorders of the liver. The liver consists of parenchymal cells (60%) and sinusoidal cells (endothelial cells, Kupffer cells, fat storing cells and pit cells). The total number of cells of 1 mg of liver tissue is 202,000, including 171,000 parenchymal cells and 31,000 sinusoidal cells. The 300 billion parenchymal cells are in close contact with the circulating blood via the sinusoids. The sinusoidal cells are located in front of the parenchymal cells in the sinusoids and function as filters. For example, the Kupffer cells are highly mobile macrophages attached to the endothelium of the sinusoids. They remove cell debris, microorganisms and colloidal substances from the blood by phagocytosis.

The parenchymal cells do not represent a uniform cell population. They are adapted to the different supply of oxygen and substrates depending on their location in the hepatic lobule. This supply decreases on the way between the portal vein to the central vein, which results in different cell organelle and enzyme inventories. This is useful for diagnostic purposes because cell damage causes the release of soluble enzymes and the enzyme pattern measured in serum allows conclusions as to which region in the hepatic lobule was especially damaged. For example, peripheral damage causes a stronger release of the ALT from the cell than central damage because the ALT activity is higher in the periphery of the hepatic lobule than in the center.

The name “aminotransferase” describes the function of the enzymes AST and ALT, i.e. the transfer of the NH2 group of amino acids to keto acids, preferably α-ketoglutarate. In this manner, the amino groups of the different amino acids are collected in a single amino acid, preferably glutamate, during the amino acid catabolism. In a subsequent series of reactions, for example oxidative desamination, the nitrogen is removed from the glutamate and converted to excretable nitrogenous compounds.

Liver, myocardium and skeletal muscle have a relatively high AST activity compared to other tissues. Therefore, they are almost always the tissues of origin of elevated AST activity.

The specific activity of ALT is about 10-fold higher in the liver than in the myocardium and skeletal muscle; hence, the ALT is considered a liver-specific enzyme. It is suited for use as screening enzyme for detecting liver diseases.

The AST and ALT are located in parenchymal and non-parenchymal cells of the liver. The ALT only dissolves in cytoplasm, has a molecular weight of about 110 kDa and its activity in the hepatocyte is 2800-fold higher than in serum. The AST is a dimeric molecule. The molecular weight of the dissolved form is 93 kDa and that of the mitochondrial form is 91 kDa. 30% of the AST is dissolved in cytoplasm and 70% binds to mitochondrial structures. The AST activity is 7,000-fold higher in the liver than in serum. Enzymes released from hepatocytes pass into the circulation easily and quickly because sinusoids have no basal membrane.

The enzyme pattern appearing in the plasma and the enzyme activities in liver disease are dependent on the nature of the damage.

In acute viral hepatitis, almost all cells of a hepatic lobule are affected. There is a mild inflammation of the hepatocytes associated with disturbance of cell membrane permeability, and cytoplasmic ALT and AST pass into the plasma. The AST/ALT ratio is usually below 1.0 because the amount of AST released into the plasma is smaller than that of ALT. Concerning the pathogenesis of viral hepatitis B, it is assumed that the virus itself causes little damage to the parenchymal cells. After recognition by T-lymphocytes, circulating viral antigens are thought to cause the proliferation of sessile T-lymphocytes that are directed against hepatocytes. The T-lymphocytes recognize virugenic proteins in the plasma membrane of the hepatocyte and cause their damage. This leads to increased permeability of the plasma membrane for ions resulting in colloid osmotic ballooning or even lysis of the cell.

In acute viral hepatitis, the level of the aminotransferases passing into the plasma is correlated with the amount of affected parenchymal tissue. If the hepatocellular injury is reversible, restitutio ad integrum is possible. More severe injury causes increased release of aminotransferases, especially mitochondrial AST, into the plasma. An AST/ALT ratio above 1.0 is an indicator of such processes and indicates hepatocyte necrosis.

Chronic inflammations of the liver are focal. In chronic active hepatitis, the cell necroses starting at the periportal fields only cause a moderate to medium increase in aminotransferases and LD. The AST/ALT is above 1. There is no direct correlation between the aminotransferase levels and the inflammatory activity.

The immune system of the sinusoidal cells can become insufficient in chronic liver diseases, especially in liver cirrhosis. In this case, antigens pass into the circulation. In particular, this occurs in impaired liver perfusion if the blood bypasses the liver by a spontaneous or surgical portocaval shunt. The immune response to antigens not removed by the liver causes poly clonal hypergammaglobulinemia in serum protein electrophoresis.

In alcoholic hepatitis, the serum AST is higher than the ALT. Whereas all other hepatitides cause a decrease in cytosolic and mitochondrial AST in the cells, the alcoholic form only results in a cytosolic decrease.

Obstructive jaundice and acute hypoxic hepatopathies due to impaired perfusion as well as toxic substances cause the necrosis of centroacinar parenchymal cells. This results in an over proportional increase in GLD compared to ALT.

In acute toxic liver injury with massive cell necrosis, the enzyme pattern in serum corresponds to that of the parenchymal cells: LD > AST > ALT > GLD.

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1.7 Cholinesterases (ChE)

Lothar Thomas

Vertebrates posses two Cholinesterase genes producing the enzymes acetylcholinesterase and acylcholine acetylhydrolase /1/.

The acetylcholine acetylhydrolase (EC 3.1.1.7), also referred to as acetylcholinesterase (AChE). This enzyme is present in the outer membrane of erythrocytes, in the gray matter of the central nervous system, in the sympathetic ganglia of the neuromuscular end plate, in the lung and spleen, but not in plasma. Under physiological conditions AChE performs the breakdown of acetylcholine, which is the chemical mediator responsible for the conduction of nerve impulses at the sites of cholinergic transmission. AChE hydrolyzes acetylcholine and is essentially inactive on butyrylcholine, arylesters and alcylesters.

Acylcholine acylhydrolase (EC 3.1.1.8), also referred to as cholinesterase (ChE). This enzyme is present in plasma, in the liver, intestinal mucosa, pancreas, spleen and the white matter of the central nervous system. Besides cholinesters, the ChE hydrolyzes benzoylcholine and butyrylthiocholine as well as arylesters and alcylesters. The function of this serum-specific enzyme is unknown. AChE and ChE are competitively inhibited by the alkaloids prostigmine and physostigmine. The following description only refers to ChE, i.e., the enzyme activity determined in plasma.

1.7.1 Indication

1.7.2 Method of determination

Determination of acetylcholine esterase (EC 3.1.1.7) /2/

Colorimetric method

Principle: acetylthiocholine is hydrolyzed by AChE to acetic acid and thiocholine. The catalytic activity of AChE is measured by following the increase of the yellow anion 5-thio-2-nitrobenzoate, produced from thiocholine when it reacts DTNB (DTNB, 5.5’-dithio-bis-2-nitro benzoic acid 10 mmol/L; NaHCO3 17.85 mmol/L = buffered Ellman’s reagent).

Benzoylcholine method /3/

Principle: benzoylcholine is hydrolyzed by AChE to benzoic acid and choline. The reduction in absorption of benzocholine is measured at 240 nm.

Proposal of Standard Method for the Determination of Cholinesterase (EC 3.1.1.8) at 37 °C /4/

Principle: butyrylthiocholine is hydrolyzed by CHE to butyric acid and thiocholine (Tab. 1.7-1 – Principle of CHE determination and calculation of dibucaine number). Thiocholine instantly reduces yellow hexacyanoferrat(III) to almost colorless hexacyanoferrat (II), thus allowing the direct spectrometric monitoring of the reaction (Tab. 1.7-2 – Chromogenic reactions for measuring the thiocholine produced).

1.7.2.1 Phenotyping of genetic variants

The synthesis of ChE in plasma is controlled by a gene locus on the long arm of chromosome 3.

The alleles U, A, S, F, H, J, K have been identified and are known to be responsible for the synthesis of potentially 28 phenotypes /15/.

Identical genotypes may have different phenotypes because some individuals have more than one mutation in the same gene. The UA phenotype, for example, can correspond to the two genotypes UA and UAK.

Up to 45 different diploid genotypes, but only 11 different phenotypes are possible /6/. Some of the ChE variants (Tab. 1.7-8 – Biochemical characteristics of cholinesterase variants) cause lower ChE activity in plasma, do not hydrolyze succinylcholine and cause extended apnea after surgery during which succinylcholine-type muscle relaxants are administered.

Inhibition assays with dibucaine and fluoride are the classic method for biochemical phenotyping of ChE variants in plasma.

Dibucaine inhibition

Principle: In the presence of the local anesthetic dibucaine, the activity of normal ChE is inhibited more strongly than that of genetic ChE variants.

Based on the extent of inhibition, individuals are assigned to the following three groups /7/:

Using the benzoylcholine method, the ChE activity is determined in the presence and absence of 1 × 10–5 mol/L dibucaine /7/. The approach using acetylthiocholine esters as a substrate is not as common /8/.

The dibucaine number is calculated using the equation shown in Tab. 1.7-1 – Principle of CHE determination and calculation of dibucaine number.

Fluoride inhibition

This assay is used to determine the fluoride-resistant ChE variants (Tab. 1.7-8 – Biochemical characteristics of cholinesterase variants). The determination is performed corresponding to the dibucaine number; the fluoride concentration in the assay medium is 5 × 10–5 mol/L /9/.

Ro 2-0683 inhibition

Ro 2-0683 is a more selective inhibitor than dibucaine. Normal ChE (E1U) is inhibited by almost 100%, while the atypical variant (E1a) is not inhibited at all /5/.

1.7.3 Specimen

Serum, heparin anticoagulated blood: 1 mL

1.7.4 Reference interval

Refer to Tab. 1.7-3 – Cholinesterase reference intervals.

1.7.5 Clinical significance

ChE reductions are common in liver disease, can be drug-induced, occur in pesticide poisoning or, more rarely, are hereditary.

1.7.5.1 ChE in liver disease

ChE is synthesized in the liver and released into the plasma. The activity in serum depends on the adequate function and amount of liver parenchymal cells. Therefore, the ChE activity is a biomarker used to measure the global liver function. The ChE is only decreased below the lower reference limit in severe liver injury associated with reduced protein synthesis of the parenchymal cells or based on a pronounced reduction in parenchymal cell mass /12/.

The isolated determination of the ChE is generally not very efficient in the diagnosis of liver disease. For example, the positive predictive value of a pathological finding is only 21% at a prevalence of 8% of patients with liver disease in the clinical patient material, while the negative predictive value of the normal finding excluding liver disease is 97% /13/. Despite the low positive predictive value, the ChE has the following diagnostic significance (Tab. 1.7-4 – Liver diseases possibly associated with decreased ChE activity):

ChE synthesis and albumin synthesis in the liver are coupled with each other. Therefore, changes in the ChE level not induced by the liver have no corresponding match in the behavior of the albumin concentration in serum. The diagnostic information shown in Tab. 1.7-5 – Differential diagnostic significance of combined determination of ChE and albumin can be derived from the behavior of albumin and ChE in serum.

The ChE activity of more than 50% of patients with alcoholic steatosis of the liver is within the upper reference range or slightly elevated /15/. Further diseases are shown in Tab. 1.7-6 – Other diseases possibly associated with reduced ChE activity.

1.7.5.2 Drug-induced ChE inhibition

The ChE is reversibly inhibited by the alkaloids prostigmine and physostigmine. The two alkaloids compete with the choline residue of acetylcholine for the binding site at the enzyme. Other drug and substances have an irreversible inhibitory effect on the ChE. A list of drugs is shown in Tab. 1.7-7 – Drug-induced inhibition of cholinesterase.

1.7.5.3 ChE in pesticide poisoning

Organophosphates and carbamates are used worldwide as pesticides. Poisoning with these substances is a problem and especially affects pesticide applicators and children. It is estimated that three million cases of poisoning and about 200,000 deaths occur worldwide every year /22/. Pesticides are also highly toxic for humans and can cause intended and unintended poisoning /23/.

Organophosphates: organophosphates are organic phosphoric acid esters, also referred to as alkyl phosphates, such as ethyl parathion, methyl parathion, demeton-S-methyl sulfoxide, carbophention, mevinphos, chlorpyrifos, dimethoate, naled, EPBP, phosalone. The inhibitory effect of the organophosphates is irreversible and can be different in vitro and in vivo. For example, malaoxon, the highly toxic form of malathione, only forms by oxidation after uptake in the body /24/.

Carbamates: formetanate HCl, methomyl, carbaryl. The inhibitory effect of the carbamates is reversible. Together with acetylcholine esterase, carbamates form an acetylcholine esterase-carbamate intermediate. Since this intermediate is soon subject to hydrolysis, the active enzyme is available again relatively quickly.

Mode of action of the organophosphates and carbamates: organophosphates and carbamates inhibit AChE in the neural tissue and erythrocytes and the CHE in plasma. The inhibition results in the accumulation of the acetylcholine. Concentrations of 20–30 μg/L in plasma are measured. The clinical symptoms of organophosphate poisoning are based on the stimulation of the muscarine- and nicotine-sensitive acetylcholine receptors of the muscles and CNS synapses. The inhibition of the ChE in serum is insignificant under toxicological aspects, but its declining activity in organophosphate poisoning allows conclusions by analogy regarding the remaining AChE activity.

Cholinergic poisoning is commonly treated by the administration of:

Acute intoxication

The pesticides enter the body by gastrointestinal, respiratory and ocular uptake, via the skin, but most quickly by inhalation. The pesticides are quickly distributed throughout the body and accumulate in adipose tissue, liver and kidneys. Clinical symptoms occur within 12 hours unless the organophosphate is lipophilic (fenthione) or subject to metabolic activation (parathion). If the phosphoric acid esters are lipophilic, clinical symptoms start later and elimination takes several days. Clinical symptoms of organophosphate and carbamate poisoning are miosis, hyper salivation, nausea, vomiting, increased muscle tremor and sweating. The six most common symptoms in children are diarrhea, vomiting, miosis, bronchial hypersecretion, sweating and hypothermia /25/. The clinical symptoms occur if the ChE decreases to ≤ 60% of the lower reference limit following uptake of the pesticide.

Organophosphate intoxications are classified as follows based on the percentage of decrease in ChE activity /26/:

In untreated cases, the ChE returns to activity within the reference interval 30–40 days after complete inhibition. This was shown by a study /25/ on children, who had ChE levels of 10–30% the lower reference limit on admission to hospital.

Acute carbamate poisoning is less severe than organophosphate poisoning. In many cases, it is self-limiting because active AChE is quickly available again due to spontaneous lysis of the acetylcholine esterase-carbamate intermediate.

Chronic exposure to pesticides

Chronic exposure can be asymptomatic or have non-specific symptoms such as diarrhea, weight loss, myasthenia and psychic symptoms.

Monitoring of exposed individuals

Monitoring of pesticide applicators can be performed by determining the ChE in serum or in the erythrocytes according to the following recommendation /27/: Before work with the pesticides starts, determine two basic levels at intervals of 3 to a maximum of 14 days if spraying is performed for more than 6 days a month. Then perform three determinations at monthly intervals. The relative risk of pesticide poisoning is increased in workers whose initial baseline serum levels are low or if there levels had already decreased to 60–80% of their baseline previously in the season.

1.7.5.4 ChE reduction by atypical variants

The biosynthesis of cholinesterase is controlled by 4 allelic genes at locus E1 and by rare genetic variants (Tab. 1.7-8 – Biochemical characteristics of cholinesterase variants).

The control is as follows /5/:

Besides the important genotypes mentioned, the four allelic genes can form further genotypes as shown in Tab. 1.7-7 – Drug-induced inhibition of cholinesterase.

Furthermore, there are the J, K and H genes. These three genes encode normal catalytic activity of the ChE molecule. However, there are fewer molecules in the plasma because of impaired synthesis or ChE instability. For example, the K variant is associated with a reduction in ChE activity by 33%, the J variant with a reduction by 66% and the H variant with a reduction by 90%.

Reduced ChE activities are clinically significant in patients treated with the neuromuscular blocker succinylcholine in surgical interventions. Upon administration of 1–1.5 mg succinylcholine per kg of body weight at normal ChE activity in plasma, this dose is hydrolyzed by AChE within 15 minutes. Pronouncedly reduced AChE or the presence of atypical ChE result in a significant relative overdose of succinylcholine and prolonged return to normal neuromuscular function. In a study /28/ analyzing 1,247 patients with abnormal response to succinylcholine, an explanation was found in 61.1% of the cases. The genotype was normal in 28.5%, abnormal in 46.5% and could not be determined in 24.9% of the cases.

The times elapsing until neuromuscular function is restored were as follows:

The presence of a single genetically variant allele does not necessarily lead to prolonged neuromuscular failure following the administration of succinylcholine. This is, however, the case in a heterozygous combination if /6/:

Instead of biochemical inhibition using dibucaine, fluoride or Ro 2-0683 for evaluation a ChE variant, it is recommended to perform a molecular genetic DNA analysis to precisely identify the mutation underlying the atypical ChE /29/.

1.7.5.5 Elevated ChE activity

Elevated ChE activities have no diagnostic significance. Tab. 1.7-9 – Diseases possibly associated with elevated ChE activity shows diseases that may be associated with elevated ChE.

1.7.6 Comments and problems

Method of determination

Butyrylthiocholine is the most common substrate used in ChE assays for liver function assessment. The benzoylcholine method is preferred for determining the dibucaine and fluoride numbers. The ChE concentration can also be determined using immunological methods.

Reference interval

The serum activity of the ChE during the neonatal period and the following weeks is only about 50% of that in adults. It then gradually rises, reaches adult levels at the age of 6, stabilizes until puberty and remains constant furthermore. Reported age-dependent changes remain within ranges of no clinical significance. The inter individual serum concentration depends on body weight, height and gender.

The serum concentration in postmenopausal women is reported to be about 15% higher than in premenopausal women.

The ChE activity decreases by 20–30% in the first trimenon of pregnancy, remains at this level throughout pregnancy and returns to normal a few weeks after delivery.

The intake of oral contraceptives containing ethinylestradiol can lower the ChE activity by 20%.

Half-life

Half-life is 10 (3.4–12) days in circulation /30/. Since the indication of changes in liver function is substantially delayed, the ChE is not an acute parameter.

Interference factors

Hemolysis: hemolysis simulates elevated ChE if acetylthiocholine is used as a substrate because the measurement also includes the AChE from erythrocytes. If the ChE assay is performed using the recommended standard method with butyrylthiocholine, there is no interference by hemolysis due to the small volume of the sample /10/.

Lipemia: No interference (small sample volume) /10/.

Hyperbilirubinemia: No interference at concentrations of up to 10 mg/dL (170 μmol/L); the sample must be diluted if concentrations are higher /10/.

Stability

The ChE is very stable. It remains stable for up to 1 year at room temperature (20 °C) or deep-frozen in serum /31/.

1.7.7 Pathophysiology

ChE in plasma is a tetrameric glycoprotein consisting of four identical subunits. Each subunit has 574 amino acids, 9 sugar chains and an active center. The four subunits are held together by disulfide bonds and hydrophobic, non-covalent forces /6/.

Vertebrates have two cholinesterase genes responsible for AChE and CHE enzyme synthesis. They differ in substrate specificity. The CHE hydrolyzes acetylcholine and butyrylthiolcholine, the AChE only hydrolyzes acetylcholine. The size of the acyl pocket in the active center of the two enzymes is the reason for this difference. The two bulky phenylalanine side chains of the butyrylthiocholine do not fit in the acyl pocket of the AChE.

The AChE has two main characteristics enabling it to hydrolyze acetylcholine soon after release by the cholinergic synapses:

Drugs such as ecothiopate used for glaucoma treatment and cytotoxic drugs such as cyclophosphamide inhibit the AChE irreversibly by binding to an OH group of the serine in the active center of the enzyme. These substances are effective throughout the enzyme’s lifetime of several weeks and only become ineffective when new enzymes are synthesized in the liver.

Drugs binding to the active center via ionic or hydrogen bridging cause reversible inhibition. These are substances possessing a quarternary nitrogen atom, such as hexafluoronium.

Organophosphates and carbamates are a further group of ChE inhibitors. They are also referred to as anti cholinesterases. These substances are used as pesticides. Only organophosphates with a P = O bond have a potent ChE inhibiting effect. They are also referred to as direct inhibitors. Organophosphates with a P = S bond, for example malathion /23/ must first be metabolically converted to P = O. Therefore, they are referred to as indirect inhibitors. Clinical symptoms occur quickly in intoxication with direct inhibitors and are delayed and last longer in intoxication with indirect inhibitors. The following effects of ChE inhibitors are distinguished in clinical symptoms /21/:

The ChE inhibitors cause physiological dysfunction of the AChE. The AChE blocks the effect of acetylcholine in the transmission of nerve impulses from cholinergic nerves to the postsynaptic side of the effector. ChE inhibitors cause the pathological elevation of acetylcholine at the motor end plate and at parasympathetic and preganglionic sympathetic nerve endings. This also results in hyper excitation in the sympathetic nervous system due to the release of adrenaline and noradrenaline. Since the behavior of the ChE in serum regarding ChE inhibitors is comparable to that of AChE of cholinergic nervous endings, the inhibition of the enzyme’s activity in serum reflects the degree of inhibition at the synapses.

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13. Schmidt E, Schmidt FW. Klinik der Lebererkrankungen. In: Lang H, Rick W, Büttner H, eds. Validität klinisch chemischer Untersuchungen. Heidelberg: Springer, 1980: 92–112.

14. Guder WG. Modell Lebererkrankungen. In: Lang H, Rick W, Büttner H, eds. Validität klinisch-chemischer Untersuchungen. Heidelberg: Springer, 1980: 84–91.

15. Schenker S, Halff GA. Nutritional therapy in alcoholic liver disease. Semin Liver Dis 1993; 13: 196–209.

16. Toro FI, Deibis L, Machado IV, Colmenares C, Bianco NE, de Sanctis JB. Serum cholinesterase activity in viral hepatitis. Med Sci Res 1997; 25: 441–2.

17. Schmidt E, Schmidt FW. Klinische Diagnostik von Lebertumoren. Verh dt Krebs-Ges 1984; 5: 459–70.17.

18. Al-Kassab AS, Vijayakumar E. Profile of serum cholinesterase in systemic sepsis syndrome (septic shock) in intensive care units. Eur J Clin Chem Clin Biochem 1995; 33: 11–4.

19. Tromm A, Hüppe D, Than I, Schwegler U, Kuntz HD, Krieg M, May B. Die Serumcholinesterase als Aktivitätsparameter bei chronisch-entzündlichen Darmerkrankungen. Z Gastroenterol 1992; 30: 449–53.

20. Goedde HW, Benkmann HG, Das PK, Agarwal DP, Lang H, Würzburg U, Beckmann R. Activity of creatine kinase isoenzyme MB in serum and red cell acetylcholinesterase variants in patients with Duchenne muscular dytrophy. Klin Wschr 1977; 55: 215–7.

21. Jokanovic M, Maksimovic M. Abnormal cholinesterase activity: understanding and interpretation. Eur J Clin Chem Clin Biochem 1997; 35: 11–6.

22. O’Malley M. Clinical evaluation of pesticide exposure and poisoning. Lancet 1997; 349: 1161–6.

23. Stalikas CD, Konidari CN. Analytical methods to determine phosphonic and aminoacid group-containing pesticides. J Chromatogr A 2001; 907: 1–19.

24. Rodriguez OP, Muth GW, Berkman CE, Kim K, Thompson CM. Inhibition of various cholinesterases with the enantiomers of malaoxon. Bull Envir Contam Toxicol 1997; 58: 171–6.

25. El-Naggar AR, Abdalla MS, El-Sebaey AS, Badawy SM. Clinical findings and cholinesterase levels in children of organophosphates and carbamates poisoning. Eur J Pediatr 2009; 168: 951–6.

26. Okonek S. Aktuelle Gesichtspunkte zur Intoxikation durch Alkylphosphate. Internist 1975; 16: 123–30.

27. Fillmore CM, Lessenger JE. A cholinesterase testing program for pesticide applicators. JOM 1993; 35: 61–70.

28. Jensen FS, Viby-Mogensen J. Plasma cholinesterase and abnormal reaction to succinylcholine: twenty years experience with the Danish Cholinesterase Research Unit. Acta Anaesthesiol Scand 1995; 39: 150–5.

29. La Du BN. Butyrylcholinesterase variants and the new methods of molecular biology. Acta Anaesthesiol Scand 1995; 39: 139–41.

30. Huizenga JR, van de Belt K, Gips CH. The effect of storage at different temperatures on cholinesterase activity in human serum. J Clin Chem Clin Biochem 1985; 23: 283–5.

31. Ostergaard D, Viby-Mogensen J, Hanel HK, Skovgaard LT. Half-life of plasma cholinesterase. Acta Anaesth Scand 1988; 32: 266–9.

32. Massoulie J, Anselmet A, Bon S, Krejci E, Legay C, Morel N, Simon S. Acetylcholinesterase: C-terminal domains, molecular forms and functional localisation. J Physiol (Paris) 1998; 92: 183–90.

1.8 Creatine kinase (CK)

Lothar Thomas

The CK is a dimeric molecule encoded by genes whose products are CK-M, CK-B and CK-Mi. The CK-Mi is only located in the mitochondria. The activity of CK in serum comprises the cytoplasmic isoenzymes CK-MM, CK-MB, CK-BB. The CK activity in healthy individuals predominantly consists of CK-MM; the CK-MB and CK-BB only exist in traces or are not detectable. If the activity of the CK or one of the isoenyzmes is elevated, the isoenzyme pattern allows conclusions as to the underlying tissue damage.

1.8.1 Indication

If troponin is not available, as secondary biomarker in patients /1/:

1.8.2 Method of determination

IFCC Primary Reference Procedure for the Measurement of Catalytic Activity Concentrations of Creatine Kinase (CK) at 37 °C /2/

Principle: The CK (EC 2.7.3.2) catalyzes the reversible phosphorylation of creatine by ATP as shown in Tab. 1.8-1 – Principle of CK determination. Mg2+ is an obligate activating ion to form the ATP- and ADP-Mg2+ complexes. The hexokinase catalyzes the phosphorylation by ATP to form glucose-6-phosphate (G-6-P) and regenerates ADP for the CK reaction. The G-6-P is then oxidized with NADP+ to form 6-phospho gluconic acid and NADPH. The rate of NADPH formation is a measure of CK-activity of the phosphate group of phosphocreatine to Mg-ADP (Tab. 1.8-1 – Principle of CK determination).

Determination of the CK-MB concentration /3/

The CK-MB is determined by an immunochemical method.

Principle: Direct measurement of CK-B subunit at 37 °C by inhibiting M subunits with M subunit antibody.

1.8.3 Specimen

1.8.4 Reference interval

See Tab. 1.8-2 – Reference intervals of CK.

1.8.5 Clinical significance

CK in muscle injury

In most cases, the CK in the serum of healthy individuals corresponds to the activity of the muscle-specific isoenzyme CK-MM and therefore acts as a specific enzyme for the detection of muscle damage. However, activities within the reference interval do not exclude myopathy, and elevated activities can have physiological causes. Monitoring, and in unclear symptoms, the determination of the CK isoenzymes make it easier to determine whether the myocardium or skeletal muscle are affected. In hereditary skeletal muscle diseases the CK levels are higher than 1,000 U/L in neuropathic skeletal muscle diseases the levels are below 1,000 U/L.

CK in acute myocardial infarction (AMI)

The blood concentration of the CK increases following AMI (e.g., onset of infarction) and reaches pathological levels in 50% of the patients on average after 4–5 hours /9/. The CK is elevated on a regular basis within the diagnostic time frame of 8–24 hours following AMI and then – with great inter individual fluctuations – decline again to within the reference interval. The maximum CK activity rarely rises beyond 7500 U/L in AMI. Higher CK activities suggest concurrent disease of skeletal muscle. The recurrent elevation of CK and CK-MB indicates secondary trauma or reinfarction.

CK-MB concentration in acute myocardial infarction

In AMI, the profile of CK-MB is similar to that of the CK. The CK-MB reaches pathological concentrations in 50% of the patients after 3–4 hours /910/, but declines earlier than the CK. AMI can be excluded if the CK-MB does not increase within the diagnostic time frame. The half-lives of the CK isoenzymes are shown in Tab. 1.8-3 – Half-lives and time of maximum activity in hours (h) after myocardial infarction.

Early recanalization (spontaneous recovery or therapeutic success) is recognized based on a rapid increase and early peak of the CK-MB concentration occurring within 16 hours. If samples are analyzed that were taken outside the narrow diagnostic time frame, the CK-MB can still, or already again, be within the reference interval.

The determination of CK-MB in diagnosing myocardial injury has the disadvantage that the CK-MB can also be released from non-cardiac muscle in some cases.

CK in myopathies

Myopathies are diseases of skeletal muscle. They can be congenital or acquired and occur already at birth or at a later age. Clinical symptoms are hypersensitivity, myalgia and myasthenia; the CK activity is normal or elevated /11/. The following distinctions are made:

The behavior of the CK and CK isoenzymes is shown for:

1.8.6 Comments and problems

Determination of CK activity

The addition of N-acetyl cysteine to the reaction mixture reactivates the CK and protects it from oxidation processes. This requires a certain amount of time (lag-phase time). The reaction mixture also contains AMP and diadenosine pentaphosphate, thus suppressing interference by adenylate kinase (EC 2.7.4.3) from the erythrocytes, muscle, liver and platelets. EDTA stabilizes the CK and prevents possible inhibition by Ca2+ of the sample. Critical parameters of the determination are the (re)activation time, sample volume ratio and lag-phase time /25/. An activation time of 180 sec. is sufficient for an exact measurement of new samples. An activation time of 300 sec. may be necessary for older samples and some quality assessment specimens. It is recommended to start the reaction process by addition of the substrate; start by addition of serum is possible /25/.

CK-MB concentration

Interferences: besides interference typical of immunoassays, for example by human anti-mouse antibodies or high biotin doses, interference by CK-B-binding autoantibodies can occur /12/. The presence of macro CK does not interfere with the assay determination.

Reference interval

The re-evaluation of the reference interval for adults was obtained in hospitalized subjects /245/. This explains the lower levels compared to an outpatient cohort. The reference intervals for children were determined using a procedure adapted to the IFCC reference method /7/. In this method, the thiol compounds of the reagent show the strongest deviations. Hence, the values for younger children (higher proportion of CK-B) cannot be applied to the IFCC method without reservation.

Macro CK (see also Tab. 1.1-2 – Macroenzymes: Characterization, clinical significance and laboratory findings)

The prevalence of the macro CK in elevated serum CK activity is about 2% /13/. Macro CK type 1, a complex of immunoglobulin and CK, is the most common form. Exact evidence can only be provided by procedures where the molecular weight is determined, for example exclusion chromatography, gradient gel electrophoresis. Treatment of the serum with polyethylene glycol gives initial clues.

Stability

Serum samples and reference specimens not processed within 12 hours should be stored well sealed and dark. In that case, the activity will not change within 3 days at 4 °C and within 4 weeks at –20 °C /14/.

1.8.7 Pathophysiology

The enzymes CK and adenylate kinase are of vital importance for the synthesis of ATP, the immediate energy source of the tissues.

The CK participates in the energy supply to the muscle in two ways (Fig. 1.8-1 – Involvement of CK and adenylate kinase (AK) in energy production in the muscle). In the mitochondria, the site of energy production, the mitochondrial CK catalyzes the synthesis of phosphocreatine (PCr) from ATP. The high-energy PCr is then transported from the mitochondria to the cytoplasm by the PCr shuttle, where it is reconverted to ATP by CK at the sites of energy consumption (muscle contraction, ion channels of the membrane, syntheses) /1516/. The CK is present intracellularly in the free form or associated to corresponding cell structures.

Three cytoplasmic CK isoenzymes can be isolated from human tissue as dimers that can consist of the subunits M (M, muscle) and B (B, brain). Their gene loci are on chromosome 14 (B subunit) and the long arm of chromosome 19 (M subunit) /17/. The two mitochondrial CK isoenzymes are referred to as S-MTCK (sarcomeric) and U-MTCK (ubiquitous). In addition, there are inconsistent abbreviations for the dimeric form such as CK-MiMi, mCK, CK-MT or CKmito. The CK monomers with a molecular weight of 40 kDa consist of approximately 360 amino acids and contain SH groups. Hybridization between the M and B subunits that are already active as monomers results in CK-MB. There is no hybridization with the Mi subunit /18/.

Based on their distribution to specific tissues, the isoforms are referred to as muscle type (CK-MM), myocardial type (CK-MB), brain type (CK-BB) and mitochondrial type (CK-MiMi). Despite these designations, the tissue specificity of these isoenzymes is not very high. CK-BB is an ubiquitous isoenzyme that has its highest activity in the brain. Similarly, the predominant amount of CK-MB is found in skeletal muscle and only its highest concentration is located in the myocardium. There is very different data on the quantitative distribution of the CK isotypes in the tissues /19/. Tab. 1.8-8 – Tissue distribution of CK isoenzymes provides a rough overview of the distribution.

Since the CK enters the blood in the event of tissue injury, the isoenzyme pattern of the blood reflects the isoenzyme pattern of the damaged tissue. This statement is qualified by the following facts:

Having been released into the blood, the CK is subject to post synthetic modifications that lead to the CK isoforms. Isoforms with a normal molecular weight of about 80 kDa are created if the carboxypeptidase gradually removes the C-terminal lysin of both M chains.

Isoforms with an increased molecular weight higher than 200 kDa are created if CK is bound by specific immunoglobulins (macro CK type 1) or if the CK mito is present in the preferred oligomeric form (macro CK type 2).

References

1. Thygesen K, Alpert JS, White HD, Joint ESC/ACCF/AHA/WHF Task Force for the Redifinition of Myocardial Infarction. J Am Coll Cardiol 2007; 50: 2173–95.

2. IFCC Primary Reference Procedures for the Measurement of Catalytic Activity Concentrations of enzymes at 37 °C. Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase. Clin Chem Lab Med 2002: 40: 635–42.

3. Christenson RH, Vaidya H, Landt Y, Bauer RS, Green SF, Apple FA, et al. Standardization of creatine kinase-MB (CK-MB) mass assay: the use of recombinant CK-MB as a reference material. Clin Chem 1999; 45: 1414–23.

4. Thomas L, Müller M, Schumann G, Weidemann G, Klein G, Lunau S, Pick KH, Sonntag O. Consensus of DGKL and VDGH for interim reference intervals on enzymes in serum. J Lab Med 2005; 29: 301–8.

5. Schumann G, Klauke R. New IFCC reference procedures for the determination of catalytic activity concentrations of five enzymes in serum: preliminary upper reference limits obtained in hospitalized subjects. Clin Chim Acta 2003; 327: 69–79.

6. Stein W. Laboratory diagnosis of acute myocardial infarction. Darmstadt: GIT-Verlag, 1988.

7. Ghoshal AK, Soldin SJ. Evaluation of the Dade Behring Dimension RxL: integrated chemistry system-pediatric reference ranges. Clin Chim Acta 2003; 331: 135–45.

8. Apple FS, Quist HE, Doyle P, Otto AP, Murakami MM. Plasma 99th percentile reference limits for cardiac troponin and creatine kinase MB mass for use with European Society of Cardiology/American College of Cardiology consensus recommendations. Clin Chem 2003; 49: 1331–6.

9. Mair J, Smidt J, Lechleitner P, Dienst F, Puschendorf B. Equivalently early sensitivity of myoglobin, creatine kinase MB mass, creatine kinase and creatine kinase MB mass, creatine kinase isoform ratios, and cardiac troponins I and T for acute myocardial infarction. Clin Chem 1995; 41: 1266–72.

10. Zaninotto M, Altiner S, Lachin M, Carraro P, Plebani M. Fluoroenzymometric method to measure cardiac troponin I in sera of patients with myocardial infarction. Clin Chem 1996; 42: 1460–6.

11. Pasternak RC, Smith SC, Jr, Bairey-Merz CN, Grundy SM, Cleeman JI, Lenfant C. ACC/AHA/NHLBI clinical advisory on the use and safety of statins. J AM Coll Cardiol 2002; 40: 567–62.

12. Stein W, Bohner J. Influence of autoantibodies to creatine kinase-BB on assays for MB isoenzyme. Clin Chem 1985; 31: 1189–92.

13. Fahie-Wilson MN, Burrows S, Lawson GJ, Gordon T, Wong W, Dasgupta B. Prevalence of increased serum creatine kinase activity due to macro-creatine kinase and experience of screening programmes in district general hospitals. Ann Clin Biochem 2007; 44: 377–83.

14. ECCLS European Committee for Clinical Laboratory Standards. Standards for enzyme determination. Creatine kinase, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase. Lund: ECCLS Central Office, document number 3–4, 1988.

15. Wallimann T. Bioenergetics: dissecting the role of creatine kinase. Curr Biol 1994; 4: 42–6.

16. Wallimann T, Hemmer W. Creatine kinase in non-muscle tissues and cells. Mol Cell Biochem 1994; 133–4: 193–220.

17. Stallings RL, Olson E, Strauss AW, Thompson LH, Badinski LL, Siciliano LJ. Human creatine kinase genes on chromosomes 15 and 19, and proximity of the gene for the muscle form to the genes for apolipoprotein C2 and excision repair. Am J Hum Genet 1988; 43: 144–51.

18. Payne RM, Strauss AW. Expression of the mitochondrial creatine kinase genes. Mol Cell Biochem 1994; 133–4: 235–43.

19. Lang H. Creatine kinase isoenzymes. Heidelberg: Springer, 1981.

20. Ravkilde J, Nissen H, Hørder M, Thygesen K. Independent prognostic value of serum creatine kinase isoenzyme MB mass, cardiac troponin T, and myosin light chain levels in suspected acute myocardial infarction. Analysis of 28 months of follow-up in 196 patients. J Am Coll Cardiol 1995; 25: 574–81.

21. Farah SY, Moss DW, Ribeiro P, Oakley CM, Sapsford RN. Interpretation of changes in the activity of creatine kinase MB isoenzyme in serum after coronary artery bypass grafting. Clin Chim Acta 1984; 141: 219–25.

22. Eltze C, Hildebrandt G, Johanson M. Über das Verhalten der Creatin-Kinase im Serum bei Muskelkater. Klin Wochenschr 1983; 61: 1147–51.

23. Manfredi TG, Fielding RA, O’Reilly KP, Meredith CN, Lee HY, Evans WJ. Plasma creatine kinase activity and exercise-induced muscle damage in older men. Med Sci Sports Exerc 1991; 23: 1028–34.

24. Lippi G, Schena F, Montagnana M, Salvagno GL, Guidi GC. Influence of acute physical exercise on emerging muscular biomarkers. Clin Chem Lab Med 2008; 46: 1314–8.

25. McMahon GM, Zeng X, Waikar SS. A risk prediction score for kidney failure or mortality in rhabdomyolysis. JAMA Internal Medicine 2013; 173: 1821–7.

26. Mohassel P, Mammen AL. The spectrum of statin myopathy. Curr Opin Rheumatol 2013; 25: 747–52.

27. Hackl W, Mauritz W, Schemper M, Winkler M, Sporn P, Steinbereithner K. Prediction of malignant hyperthermia susceptibility: statistical evaluation of clinical signs. Br J Anaesth 1990; 64: 425–9.

28. Arzneimittelkommission der deutschen Ärzteschaft. Akute Rhabdomyolyse unter Olanzapin. Dtsch Ärztebl 2005; 102: B1974–5.

29. Pearson CM, Rimer DG, Mommaerts WFHM. A metabolic myopathy due to absence of muscle phosphorylase. Am J Med 1961; 30: 502–17.

30. Stein W, Bohner J, Bahlinger M. Creatine kinases. In: Blaton V, van Steirteghem A. Plasma isoenzymes: the current status. Basel: Karger, 1986; 95–104.

31. Stein W, Bohner J, Schüch K. Creatine kinase-BB in blood cells: a marker of myeloproliferative disorders (MPD). Clin Chem 1986; 32: 1138.

32. Nordby HK, Urdal P. Creatine kinase BB in blood as index of prognosis and effect to treatment after severe head injury. Acta Neurochirurgica 1985; 76: 131–6.

33. Chemnitz G, Bartner J. Zur Bedeutung erhöhter Kreatinkinase-Aktivität im Serum nach apoplektischem Insult. Klinisches Labor 1994; 40: 529–33.

34. Stein W. Creatinkinase. In: Thomas L, ed. Labor und Diagnose. Frankfurt; TH-Books 2008: 89–97.

1.9 Gamma-glutamyl transferase (GGT)

Lothar Thomas

The GGT is a peptidase that transfers amino acids from one peptide to the next and thus functions as amino acid transferase. The GGT activity primarily is synthesized in the hepatobiliary system, and the enzyme is elevated in serum in many hepatobiliary diseases. Studies have shown strong positive associations between GGT and cardiovascular risk factors such as smoking, components of the metabolic syndrome (obesity hypertension, lipid metabolism, type 2 diabetes). Elevated GGT is also associated with chronic kidney disease. independently of factors such as alcohol consumption /1/.

1.9.1 Indication

1.9.2 Method of determination

IFCC Primary Reference Procedure for the Measurement of Catalytic Activity Concentration of γ-Glutamyltransferase at 37 °C /2/

Principle: The GGT (EC 2.3.2.2) catalyzes the transfer of the glutamyl residue from γ-glutamyl-3-carboxy-4-nitroanilide to glycylglycine releasing 5-amino-2-nitrobenzoate (Tab. 1.9-1 – Principle of GGT determination). The increase in concentration of this substance measured as absorption increase at 405 nm is proportional to the enzyme activity in the sample.

1.9.3 Specimen

Serum, plasma (heparin, EDTA): 1 mL

1.9.4 Reference interval

See Tab. 1.9-2 – Reference intervals of GGT.

1.9.5 Clinical significance

The GGT is a liver-specific and bile duct-specific enzyme. Although other tissues also contain GGT, major elevations of the GGT not induced by the liver or bile ducts are rare.

However, the GGT is not only a biomarker for hepatobiliary diseases and excessive alcohol consumption, but also a metabolic toxic marker and an indicator of the presence of chronic diseases in asymptomatic patients. The activity of GGT in hepatobiliary diseases is shown in Tab. 1.9-4 – GGT in hepatic and biliary tract diseases and resulting from different etiologies in Tab. 1.9-5 – Various causes of elevated GGT levels.

1.9.5.1 Elevated GGT /5/

Drugs and alcohol: patho biochemically, both drugs and alcohol cause an induction of GGT synthesis. It must be kept in mind that there is great inter individual variation in enzyme induction.

Drugs, especially anticonvulsives (phenobarbital, phenytoin), psychotropic drugs, steroid hormones, anticoagulants, streptomycin, xenobiotics and carcinogens (nitrosamines), cause 1.5–3-fold elevations above the upper reference limit. Elevations due to other drugs such as streptokinase and oral contraceptives are not as high.

Alcohol in doses as low as 0.75 g/kg BW can cause elevated GGT within one day; the GGT is about 25% of the initial level after 2.5 days and returns to the initial level after 4 days. However, these elevations mainly remain within the reference interval.

Cholestasis syndromes: cholestasis is associated with structural changes of the cell membrane leading to the detachment of GGT located at the surface. In addition, GGT increasingly formed by induction no longer attaches to the cell membrane and immediately enters the circulation. Cholestasis can occur in acute and chronic hepatitis and in chronic liver diseases of other causes. In cholestasis, the GGT is elevated more than 5-fold the upper reference limit in many cases, while the GGT elevations found in acute and chronic hepatitides of viral genesis are not higher than 3–5-fold the upper reference limit.

Predictor for risk of disease: The GGT shows association with vascular and metabolic diseases and generally with morbidity and mortality. This association is independent of potentially concurrently present hepatic disease or alcohol abuse. The GGT is positively associated with /1/:

The associations make the GGT a predictor for cardiovascular diseases and increased mortality. The GGT level is also associated with chronic renal disease, independently of alcohol consumption. The GGT levels are moderately elevated or range within the upper third of the reference interval. In a study /6/, GGT levels above 24 U/L were associated with increased myocardial infarction mortality. In a different study /7/, the incidence of diabetes mellitus type 2 was 3 times higher and that of a metabolic syndrome was 4 times higher in individuals with GGT levels of 36–50 U/L.

1.9.5.2 Diagnostic sensitivity and specificity of GGT for liver diseases

Since elevated GGT is triggered by numerous chronic diseases and also by primary liver injury, they have a good tissue specificity and high diagnostic sensitivity, but only a low specificity for hepatobiliary diseases. For example, the diagnostic sensitivity for hepatobiliary diseases is 95% at 96% specificity compared to healthy individuals and 74% compared to non-hepatobiliary disease patients. The GGT is the most frequently single elevated enzyme in hepatobiliary diseases with a proportion of 14% (6–20%); the proportion is even higher (22–30%) in individuals with isolated GGT elevations who have not been clinically diagnosed with a primary disease of the liver or bile ducts /8/. The GGT has a low diagnostic specificity for liver diseases if it is the only enzyme elevated. It does not gain in disease specificity and differential diagnostic significance until other enzymes such as the ALT and ALP are also determined.

Elevated aminotransferases at normal GGT are found in chronic liver disease.

1.9.5.3 Isolated elevation of GGT

Isolated elevations can be caused by /8/:

1.9.5.4 Differential diagnostic significance of GGT

The GGT is significant under the following aspects:

Assessment criteria are:

1.9.5.5 Differentiation of cholestasis from inflammatory liver diseases /9/

In the setting of jaundice, the ALT activity and the GGT/ALT ratio allow a rough differentiation between hepatitic and cholestatic causes. For example, the ALT levels found in patients with obstructive jaundice are not higher than 25-fold the upper reference limit and the GGT/ALT ratio is always above 1 and even above 6 in many cases (Tab. 1.9-3 – Ratio GGT/ALT in hepatobiliary diseases/9/. A more pronounced relative increase in the GGT compared to the ALP is another criterion in support of cholestatic syndrome. In intrahepatic cholestasis, the aminotransferases can be elevated with a profile approximately parallel to that of the elevated GGT and ALP so that the GGT/ALT ratio is only just above 1.

To a certain extent, the level of the GGT is diagnostically conclusive in intrahepatic cholestasis. For example /9/:

In the setting of jaundice, normal GGT and normal activity of other liver enzymes and LD suggest the presence of a bilirubin metabolic disorder.

In pediatric practice, the GGT has significant advantages over the ALP in the detection of cholestatic syndrome. The ALP is difficult to interpret in children due to age-dependent variations or possible vitamin D deficiency /10/.

1.9.5.6 GGT as biomarker of alcoholism /1112/

GGT levels above the upper reference limit are measured in about 75% of alcohol addicts /11/. However, there is no correlation between the total quantity ingested in a certain period of time, the daily amount of intake or the duration of alcohol intake. Only 20–50% of the individuals, who daily consume large amounts of alcohol without being dependent, show elevated GGT. The GGT is a biomarker of chronic intake of larger amounts of alcohol and is not elevated in occasional drinkers after a “boozy evening” unless these individuals suffer from a liver disease /11/.

The daily consumption of more than 40 g of alcohol in habitual drinkers and at least 60 g of alcohol for at least 5 weeks in non-habitual drinkers is required before the GGT rises to pathological levels /13/. The GGT has a diagnostic sensitivity of 55–100% at 50–72% specificity in the diagnosis of chronic alcoholism /14/. Alcohol-induced elevation of the GGT in individuals under the age of 30 is rare. The diagnostic sensitivity of GGT is lower in women than in men /15/.

The GGT is suited for monitoring alcohol abstinence. Depending on the preexisting liver disease, the GGT declines with a half-life of 14–26 days and, after alcohol abstinence of 4–5 weeks, reaches the reference interval. The GLD is a good biomarker for monitoring alcohol withdrawal (see Section 1.10 – Glutamate dehydrogenase (GLD)).

1.9.6 Comments and problems

Blood sampling

GGT activity is lower in blood containing citrate, oxalate or fluoride than in serum.

Method of determination

The activities measured in heparin anticoagulated blood using the IFCC method (substrate γ-glutamyl-3-carboxy-4-nitroanilide) are too low /45/.

Reference interval

The upper reference limits of adults are too high because they are based on normal alcohol consumption. A presumably alcohol-induced, inter individual (but not generally intraindividual) increase in GGT levels occurs with increasing age /48/.

Hemolysis

Hemolysis leads to lower GGT levels at free Hb concentrations above 2 g/L /45/.

Half-life

The half-life is 7–10 days and, in alcoholics, up to 28 days /8/.

Macroenzymes

GGT macroenzymes are only present in hepatobiliary diseases, but have no diagnostic and differential diagnostic significance (for further information, see Tab. 1.1-2 – Macroenzymes: Characterization, clinical significance and laboratory findings).

Oral contraceptives

Elevated GGT occurs in oral contraceptives containing norgestrel or levonorgestrel as progestagen /47/.

Stability in serum

1 week at room temperature (20 °C) /49/.

1.9.7 Pathophysiology

The GGT is a heterodimeric protein each consisting of a single polypeptide chain. It is located on the cytoplasmic membrane of many somatic cells; the active center of the enzyme is directed outward. The luminal surfaces of cells with secretory or absorptive functions especially abound in GGT, but basolateral surfaces of renal tubule cells also contain GGT.

The GGT is the only enzyme that breaks down noteworthy amounts of glutathione (GSH) and GSH conjugates. In the γ-glutamate cycle, for example, it breaks down GSH (γ-glutamyl-cysteinyl-glycine), which is formed intracellularly and transported to the extracellular (luminal) side of the cell membrane, into cysteinylglycine and the γ-glutamyl residue. The transport of GSH into the extracellular compartment, the breaking down of its components by the GGT and their re-synthesis in GGT are referred to as γ-glutamate cycle (Fig. 1.9-1 – GGT and the glutamate cycle). In this way, the GGT supports the supply of GSH, the most important non-protein antioxidant, to the tissues. The reason why large amounts of GSH are secreted from the hepatocytes into the bile, from the proximal tubule cells into urine, from the type II pneumocytes into the alveoli and from the microvilli of the brush border into the intestine is to protect the cell membrane against oxidative destruction. Moreover, the GSH is the reservoir of cysteine, a relatively toxic amino acid, and its transport form in the organism; hence, the cysteine concentration is kept low /50/.

The GGT also plays an important role /50/:

Under certain conditions, however, the degradation of GSH plays a pro-oxidant role. It is assumed that the oxidation of low density lipoprotein (LDL) by the GSG/GGT-dependent reduction of iron is a mechanism in the development of atherosclerosis. The GGT is detectable in foam cells of atherosclerotic lesions of the vascular intima. This is where the GGT forms cysteinylglycine. The cysteinylglycine reduces Fe (III) and thus promotes the Fe (II)-catalyzed oxidation of LDL. The increased synthesis of oxidized LDL promotes the progression of atherosclerosis. The GGT of atherosclerotic plaques is thought to come from the plasma or from macrophages with an up regulated GGT synthesis /51/.

The serum GGT originates from the liver and is present in a heterogeneous form. Most of it binds to lipoproteins, especially to HDL and also to LDL. A small proportion is soluble in water, has a molecular weight of 84 kDa and is similar to the GGT released from the hepatocyte membrane by proteases /52/.

The HDL-bound GGT is predominant in non-icteric liver diseases. The GGT bound to LDL is elevated in cholestasis, and the water-soluble form is elevated in all kinds of hepatopathies. The latter never exceeds a proportion of 20% in the total activity. It is assumed that the HDL-bound and LDL-bound GGT is released due to the solubilization of hepatocyte membranes by bile or as part of a membrane fragment following cell rupture. The water-soluble form is thought to be released from the cell membrane directly by proteases. The proteases dissociate the hydrophilic, enzymatically active part from the hydrophobic, membrane-bound domain of the enzyme /53/.

The GGT is cleared from the plasma mainly through the liver and secreted through the bile. The activity in the bile is about 10-fold higher than in plasma. A small part is catabolized by the kidneys and part is secreted with the urine.

In the fetal liver, the GGT is distributed evenly over the lobuli where it occurs dissolved in the hepatocyte and bound to the cell membrane. In the liver of adults, the GGT is located in the periphery of the lobuli and the activity of the dissolved form in the hepatocyte is low. The main proportion is located on the canalicular and sinusoidal membrane of the hepatocyte and the epithelial membrane of larger bile ducts /54/.

The synthesis of the GGT in the liver is induced by cholestasis, alcohol and drugs in therapeutic doses (e.g., phenytoin). The membrane-bound GGT propagates. The enzyme spreads mainly periportally from the canalicular membranes to the other parts of the cell membrane facing the Dissé space.

The elevated GGT measurable in serum after enzyme induction is dependent on the nature and extent of the noxa. Parenchymal damage must always be considered if the GGT is elevated more than 2-fold the upper reference limit or if the elevation occurs concurrently with an increase in other liver enzymes.

Elevated GGT in dysfunctional bile secretion can be caused by solubilization of the GGT by bile acids or an increase in GGT formation of the hepatocyte. The latter, in particular, is thought to be the reason for the GGT increase in hepatoma cells compressed by a liver tumor and in regenerating areas of the cirrhotic liver /55/. For the molecular pathogenesis of cholestasis, see Section 5.2 – Bilirubin.

References

1. IFCC Primary Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes at 37 °C. Part 6. Reference procedure for the measurement of catalytic concentration of γ-Glutamyltransferase. Clin Chem Lab Med 2002; 40: 734–8.

2. Abicht K, El-Samalouti V, Junge W, Kroll M, Luthe H, Treskes M, Klein G. Multicenter evaluation of new liquid GGT and ALP reagents with new reference standardization and determination of reference intervals (abstract). Clin Chem Lab Med 2001; 39: S346.

3. Ghoshal AK, Soldin SJ. Evaluation of the Dade Behring Dimension RxL: integrated chemistry system-pediatric reference ranges. Clin Chim Acta 2003; 331: 135–46.

4. von Herbay A, Strohmeyer G. Die erhöhte γ-GT (γ-Glutamyltransferase). Dtsch Med Wschr 1994; 119: 1041–4.

5. Haring R, Wallaschofski H, Nauck M, Dörr M, Baumeister SE, Völzke H. Ultrasonic hepatic steatosis increases prediction of mortality risk from elevated serum gamma-glutamyl transpeptidase levels. Hepatology 2009; 50: 1403–11.

6. Wannamethee G, Ebrahim S, Shaper AG. γ-glutamyltransferase: determinants and association with mortality from ischemic heart disease and all causes. Am J Epidemiol 1995; 142: 699–708.

7. Kim DJ, Noh JH, Cho NH, Lee BW, Choi JH, Jung JH et al. Serum γ-glutamyltransferase within its normal concentration range is related to the presence of diabetes and cardiovascular risk factors. Diabetic Medicine 2005; 22: 1134–40.

8. Schmidt E, Schmidt FW. Diagnostik des Ikterus. Dtsch Med Wschr 1984; 109: 139–44.

9. Schmidt E, Schmidt FW. γ-Glutamyl-Transpeptidase. Dtsch Med Wschr 1973; 98: 1572–8.

10. Cabrera-Abreu JC, Green A. Gamma-glutamyltransferase: value of its measurement in paediatrics. Ann Clin Biochem 2002; 39: 22–5.

11. Sharpe PC. Biochemical detection and monitoring of alcohol abuse and abstinence. Ann Clin Biochem 2001; 38: 652–64.

12. Schmidt E, Schmidt FW. Alkoholschäden. In: Schmidt E, Schmidt FW, Manns P, eds. Lebererkrankungen. Stuttgart; Wissenschaftliche Verlagsgesellschaft 2000: 267–86.

13. Congrave KM, Saunders JB, Whitefield JB. Diagnostic tests for alcohol consumption. Alcohol Alcohol 1995; 30: 13–26.

14. Kristenson H, Trell E, Fex G, Hood B. Serum gamma glutamyl transferase: statistical distribution in a middle aged male population and evaluation of alcohol habits in individuals with elevated levels. Prev Med 1980; 9: 108–19.

15. Whitfield JB, Hensley WJ, Bryden D, Gallagher H. Effects of age and sex on biochemical responses to drinking habits. Med J Aust 1978; 2: 629–32.

16. Schmidt E. Normale γ-Glutamyltranspeptidase bei Hepatitis? Dtsch Med Wschr 1974; 99: 1696.

17. Berg PA, Klein R. Diagnose der primär biliären Zirrhose. Dtsch Med Wschr 1988; 113: 143–5.

18. Schmidt E, Schmidt FW. Klinisch-chemische Untersuchungsmethoden. In: Schmidt E, Schmidt FW, Chemnitz G, eds. Klinik der Gegenwart. München; Urban und Schwarzenberg 1984: E 381–421.

19. Saadeh S. The spectrum of nonalcoholic fatty liver disease: from steatosis to nonalcoholic steatohepatitis. Clev Clin J Med 2000; 67: 96–104.

20. Gastaldelli A, Kozakowa M, Hojlund K, Flyvberg A, Favuzzi A, Mitrakou A, et al. Fatty liver is associated with insulin resistance, risk of coronary heart disease, and early atherosclerosis in a large European population. Hepatology 2009; 49: 1357–44.

21. Loomba R, Sirlin CB, Schwimmer JB, Lavine JE. Advances in pedriatric nonalcoholic fatty liver disease. Hepatology 2009; 50: 1282–93.

22. Börsch G, Baier J, Glocke M, Nathusius W, Gerhardt W. Graphical analysis of laboratory data in the differential diagnosis of cholestasis: a computer-assisted prospective study. J Clin Chem Clin Biochem 1988; 26: 509–19.

23. Hunt CM, Sharara AI. Liver disease in pregnancy. Amer Fam Physic 1999; 59: 829–36.

24. Lammert F, Marschall HU, Glantz A, Matern S. Intrahepatic cholestasis in pregnancy: molecular pathogenesis, diagnosis and management. J Hepatol 2000; 33: 1012–21.

25. Kelly DA. Chronic hepatitis. In: Kelly DA, ed. Disease of the liver and biliary system of children. Oxford; Blackwell 1999: 97–123.

26. Jacquemin E. Progressive familial intrahepatic cholestasis and anomalies of hepatocellular metabolism of bile acids. Arch Pediatr 1998; 5: 59–61.

27. Penn R, Worthington DJ. Is serum γ-glutamyltransferase a misleading test? Brit Med J 1983; 286: 531–5.

28. Külling D, Sauter Chr. Die Bedeutung der γ-Glutamyltransferase zur Erfolgsbeurteilung einer Chemotherapie von Lebermetastasen. Schweiz Med Wschr 1990; 120: 1435–8.

29. Lewis JH. Drug-induced liver disease. Med Clin North Am 2000; 84: 1275–1311.

30. Farrell GF. Drugs and steatohepatitis. Sem Liver Dis 2002; 22: 185–94.

31. Chitturi S, George J. Hepatotoxicity of commonly used drugs: nonsteroidal antiinflammatory drugs, antihypertensives, antidiabetic agents, anticonvulsants, lipid-lowering agents, psychotropic drugs. Sem Liver Dis 2002; 22: 169–83.

32. Stedman C. Herbal hepatotoxicity. Sem Liver Dis 2002; 22: 195–206.

33. Strohm WD. Toxische Leberschädigung und Umwelt. Krankenhausarzt 1990; 63: 411–8.

34. Sillanaukee P, Olsson U. Improved diagnostic classification of alcohol abusers by combining carbohydrate-deficient transferrin and gamma glutamyltransferase. Clin Chem 2001; 47: 681–5.

35. Naveau S, Poynard T, Zourabichvili O, Hilpert G, Naveau S, Poitrine A, et al. Prognostic value of total serum bilirubin/gamma-glutamyltranspeptidase ratio in cirrhotic patients. Hepatology 1984; 4: 324–7.

36. Meeham JJ, Geogeson KE. Prevention of liver failure in parenteral nutrition-dependent children with short bowel syndrome. J Pediatr Surg 1997; 32: 473–5.

37. Sandock DS, Seftel AD, Resnick MI. The role of gamma-glutamyl transpeptidase in the preoperative metastatic evaluation of renal cell carcinoma. J Urol 1997; 157: 798–9.

38. Sealy CH, Vonbank A, Rein P, Woess M, Beer S, Aczel S, et al. Alanine aminotransferase and gamma-glutamyl transferase are associated with the metabolic syndrome but not with angiographically determined coronary atherosclerosis. Clin Chim Acta 2008; 397: 82–6.

39. Breitling LP, Raum E, Müller H, Rothenbacher D, Brenner H. Synergism between smoking and alcohol consumption with respect to serum gamma-glutamyltransferase. Hepatology 2009; 49: 802–8.

40. Meisinger C, Döring A, Schneider A, Löwel H. Serum γ-glutamyltransferase is a predictor of incident coronary events in apparently healthy men from general population. Atherosclerosis 2006; 189: 297–302.

41. Ruttmann E, Brant LJ, Concin H, Diem G, Rapp K, Ulmer H, et al. γ-Glutamyltransferase as a risk factor for cardiovascular disease mortality. Circulation 2005; 112: 2130–7.

42. Claessen H, Brenner H, Drath C, Arndt V. Gamma-Glutamyltransferase and disability pension: a cohort study of construction workers in Germany. Hepatology 2010; 51: 482–90.

43. Kazemi-Shirazi L, Endler G, Winkler S, Schickbauer T, Wagner O, Marsik C. Gamma glutamyltransferase and long-term survival: is it just the liver? Clin Chem 2007: 53: 940–6.

44. Claessen H, Brenner H, Frath C, Arndt V. Gamma-glutamyltransferase and disability pension: a cohort study of construction workers in Germany. Hepatology 2010; 51: 482–90

45. Stromme HJ, Theodorsen L. Heparin interference in the measurement of γ-GT with the Scandinavian and the IFCC recommended method. Scand J Clin Lab Invest 1985; 45: 437–42.

46. van der Meulen EA, van Sittert NJ, Koningh AGJ, Lugtenburg D, van Strick R. General approach to correction for bias in analytical performance in longitudinal studies illustrated by estimating the effect of age on γ-glutamyltransferase activity. Clin Chem 1993; 39: 1375–81.

47. Müller-Wiegand B. Bestimmung der γ-GT mit einem gut löslichen Substrat. Lab Med 1984; 8: 158–61.

48. Schiele F, Vincent-Viry M, Fournier B, Starck M, Siest G. Biological effects of eleven combined oral contraceptives on serum triglycerides, gamma glutamyltransferase, alkaline phosphatase, bilirubin and other biochemical variables. Clin Chem Lab Med 1998; 36: 871–8.

49. Heins M, Heil W, Withold W. Storage of serum or whole blood samples? Effects of time and temperature on 22 serum analytes. Eur J Clin Chem Clin Biochem 1995; 33: 231–8.

50. Lieberman MW, Barrios R, Carter BZ, Habib GM, et al. γ-glutamyl transpeptidase. What does the organization and expression of a multipromoter gene tell us about its functions? Am J Pathol 1995; 147: 1175–85.

51. Pompella A, Emdin M, Passino C, Paolicchi A. The significance of serum γ-glutamyltransferase in cardiovascular disease. Clin Chem Lab Med 2004; 42: 1085–91.

52. Wenham PR, Horn DB, Smith AF. Multiple forms of γ-GT: a clinical study. Clin Chem 1985; 31: 569–73.

53. Grostad M, Huseby NE. Clearance of different multiple forms of human γ-glutamyltransferase. Clin Chem 1990; 36: 1654–6.

54. Köttgen E, Reutter W, Gerok W. Two different γ-GT during development of liver and small intestine: a fetal (sialo-) and an adult (asialo) glycoprotein. Biochem Biophys Res Comm 1976; 72: 61–4.

55. Tsuchida S, Hoshino K, Sato T, et al. Purification of γ-GT from rat hepatomas and hyperplastic hepatic nodules, and comparison with the enzyme from rat kidney. Cancer Res 1979; 39: 4200–4.

1.10 Glutamate dehydrogenase (GLD)

Lothar Thomas

The GLD is an enzyme of the mitochondrial matrix and present in all tissues. Its activity in the liver is 10-fold higher than in other tissues; therefore, elevated activities in serum are exclusively caused by the liver. GLD has a mostly catabolic role in humans. It catalyzes the clearance of nitrogen from the organism by releasing ammonia from glutamate. Elevated GLD levels are a marker for liver diseases with cell necrosis.

1.10.1 Indication

1.10.2 Method of determination

Proposal of Standard Methods for the Determination of Enzyme Catalytic Concentrations in serum and plasma at 37 °C. Glutamate dehydrogenase /1/

Principle: the GLD (EC 1.4.1.3) catalyzes the oxidative deamination of L-glutamate. Under assay conditions the decrease of NADH per unit of time corresponds to the catalytic concentration of the enzyme (Tab. 1.10-1 – Principle of GLD determination).

1.10.3 Specimen

Serum, plasma (heparin anticoagulated blood, EDTA, oxalate, citrate): 1 mL

1.10.4 Reference interval

See Tab. 1.10-2 – Reference intervals of GLD.

1.10.5 Clinical significance

The GLD is a liver-specific enzyme. However, it is not suited for use in screening for hepatobiliary diseases because its diagnostic sensitivity is only 47% /2/.

The practical value of GLD determination lies in the differential diagnosis of liver diseases. This is because elevated GLD in serum indicates severe parenchymal cell damage, and the activity related to the more readily released cytosolic aminotransferases is a criterion for rating the severity of acute liver injury. Compared to the ALT, which only occurs in the cytoplasm, and the AST, which is located in both the cytoplasm and the mitochondria, the GLD is:

The (ALT + AST)/GLD ratio is a differential diagnostic criterion. It is useful in the situations listed in Tab. 1.10-3 – Differential diagnosis value of the ratio (ALT + AST)/GLD.

1.10.5.1 Differential diagnosis of jaundice

The GLD is important in the differential diagnosis of jaundice, especially in acute abdomen with possible liver involvement in the form of cholecystitis or acute bile duct obstruction. The lower the (ALT + AST)/GLD ratio, the higher the probability of intrahepatic or extrahepatic mechanical cholestasis; the higher the ratio, the higher the probability of acute hepatitis. For example, extrahepatic bile duct obstruction is excluded by the following findings:

The differential diagnosis remains open if the ratio is below 50 and, in particular, below 20.

1.10.5.2 Differential diagnosis of severe liver injury /34/

The GLD is useful in differentiating between toxic and hypoxic liver injury and severe forms of acute hepatitis. In acute impaired hepatic perfusion, the activities of GLD are similar to those of the aminotransferases.

In acute endogenous or exogenous intoxication, the peak levels of the GLD are only half as high as those of the aminotransferases and, in the severe form of acute viral hepatitis, less than 5% of the aminotransferase levels. This also applies to the necrotizing form of acute viral hepatitis that may lead to acute hepatic failure. According to a study /4/, acute right heart failure, protracted septic-toxic circulatory failure and severe respiratory insufficiency are the most common causes of GLD activities higher than 25-fold the upper reference limit. The highest mean activity was found in patients with cor pulmonale following pulmonary embolism. The differentiation between the toxic and hypoxic genesis and the hepatitic genesis is possible. Toxic substances and hypoxia damage the central region of the hepatic lobule where the GLD is perivenously located.

The differential diagnosis of elevated GLD is shown in Tab. 1.10-4 – GLD in hepatic and biliary tract diseases.

1.10.5.3 Indicator of alcohol addiction

The GLD levels in alcohol-addicted individuals are substantially higher than those in individuals not addicted to alcohol. In a study /5/, healthy women and men had levels of 0.3 U/L (20 μkatal/L) and 0.6 U/L (40 μkatal/L), respectively, compared to alcoholics with levels of 4.9 U/L (296 μkatal/L) and 7.3 U/L (439 μkatal/L), respectively. The GLD is better suited for monitoring abstinence during alcohol withdrawal therapy than other biomarkers. The GLD declines more quickly than the AST and GGT during the first 7 days of abstinence, and a pronounced decrease can already be measured after 24 hours without alcohol intake.

1.10.6 Comments and problems

Method of determination

The method optimized for 37 °C is more robust than the previous one for 25 °C. It can be measured without preincubation with a longer temporal linear response. There are no blank values, and uncontrolled NADH consumption is avoided /1/.

Inhibition: Lower concentrations are measured in the presence of sodium fluoride.

Stability

GLD decreases by 10% within 24 hours at room temperature (20 °C) and by about 5% within 3 days at 4 °C.

Half-life

14–18 hours.

1.10.7 Pathophysiology

In plants and microorganisms, ammonia is incorporated directly or is produced by the metabolism of substances containing N2, NO3 and NO2. Ammonia is incorporated into L-glutamate mainly through reductive amination of 2-oxoglutarate. The physiological function of GLD is the oxidative deamination of glutamate, i.e. the enzyme catalyzes the removal of hydrogen from L-glutamate to form the corresponding ketimino acid that goes spontaneous hydrolysis to 2-oxoglutarate (the reverse reaction is used for the determination of GLD activity in vitro).

Through the release of NH3 from glutamate, GLD catalyzes the clearance of nitrogen not needed for the re-synthesis of amino acids from the organism. Reduced NAD and NADP are regenerated by the respiratory chain. Oxalacetate acting as an acceptor is catalyzed by the AST and transaminated to aspartate whose nitrogen is incorporated in the urea synthesis /6/.

The GLD is located in the mitochondrial matrix. The specific activity in the liver is about 10-fold higher than in the kidney, brain and lung and about 80-fold higher than in skeletal muscle. In the hepatic lobules, the GLD activity is about twice as high in the centrilobular zone as in the periportal zone. Therefore, in relation to acute hepatitis, toxic alcohol-induced damage or acute impaired perfusion lead to a pronounced increase in GLD compared to the aminotransferases. The increases in activity in plasma are exclusively caused by the liver.

The molecular weight of GLD in serum is 336 kDa. The GLD consists six subunits. However, polymers with a molecular weight of up to 1,000 kDa can also be found in patients with liver injury.

The GLD is significant in the differential diagnosis of liver diseases because its concentration in the centrilobular zone of the hepatic lobule is 1.8-fold higher than peripherally /7/. Being at the end of the sinusiodal supply route the centrilobular zone is at greatest risk from hypoxia and is the first area where cell damage occurs if blood flow is disturbed.

The increase in GLD in obstructive jaundice is attributed to obstruction of bile acid drainage. It is thought that this leads to damage, particularly of the mitochondria in the centrilobular region, as a result of the detergent effect of the bile acids /8/.

References

1. German Society for Clinical Chemistry. Proposal of standard methods for the determination of enzyme catalytic concentrations in serum and plasma at 37 °C. III. Glutamate dehydrogenase. Eur J Clin Chem Clin Biochem 1992; 30: 493–502.

2. Schmidt E, Schmidt FW. Enzyme diagnosis in diseases of the liver and the biliary system. In: Advances in clinical enzymology. Basel: Karger, 1979: 239.

3. Schmidt E, Schmidt FW. Diagnostik des Ikterus. Dtsch Med Wschr 1984; 109: 139–46.

4. Chemnitz G, Schmidt E, Schmidt FW, Lobers J. Diagnostische und prognostische Bedeutung massiv erhöhter Glutamat-Dehydrogenase-Aktivität im Serum. Dtsch Med Wschr 1984; 109: 1789–93.

5. Kravos M, Malesic I. Glutamate dehydrogenase as a marker of alcoholism. Alcohol&Alcoholism 2010; 45:39–45

6. Schmidt E, Schmidt FW. Enzymdiagnostik von Lebererkrankungen in der Praxis. Diagnostik 1977; 10: 348–52.

7. Schmidt E, Schmidt FW. Alkoholschäden. In: Schmidt E, Schmidt FW, Manns MP, eds. Lebererkrankungen. Stuttgart; Wissenschaftliche Verlagsgesellschaft 2000: 214–404.

8. Assel H, Fedderke J, Schmidt E, Voges S. Correlations and factor analysis of enzymes in serum of patients with hepatic metastases. In: Goldberg DM, Werner M, eds. Selected topics in clinical enzymology. Berlin: de Gruyter, 1983.

9. Lamerz P, Stieber P, Borlinghaus P, Fateh-Moghadam A. Tumor markers in cancer of the liver. Diagn Oncol 1991; 1: 363–72.

10. Kommerell B. Hepatomegalie. Diagnostik 1980; 13: 78–93.

11. Groß W, Ring K, Lodemann E, eds. Physiologische Chemie. Weinheim; VCH-Verlagsgesellschaft 1989: 214–23.

12. Guder W, Habicht GA, Kleißl J, Schmidt U, Wieland OH. The diagnostic significance of liver cell inhomogeneity: serum enzymes in patients with central liver necrosis and the distribution of GLDH in normal human liver. Z Klin Chem Klin Biochem 1975; 13: 311–8.

13. Schmidt FW. Enzymes in cholestasis. In: Bianci L, Gerok W, Sickinger K, eds. Liver and bile. Lancaster: MTP-Press, 1977: 216.

1.11 Lactate dehydrogenase (LD)

Lothar Thomas

The LD is an NAD+-oxidoreductase and catalyzes the oxidation of lactate to pyruvate using NAD+ as an H+ acceptor. The reaction is reversible and at a physiological pH the equilibrium favours the reduction of pyruvate to lactate. The total LD (EC 1.1.1.27) measurable in serum consists of the activities of the five isoenzymes LD-1 to LD-5 (Tab. 1.11-1 – Isoenzymes of LD). The isoenzyme LD-1 converts the substrate 2-oxobutyrate to hydroxy butyrate at a higher rate than the other isoenzymes and can be measured separately as hydroxy butyrate dehydrogenase.

The LD is present in varying amounts in the cytoplasm of all cells in the body. Therefore, elevated levels of total LD are found in many pathological conditions but are as such of limited diagnostic and differential diagnostic value due to lack of organ specificity. However, if the total LD is elevated, quantitative differentiation of the isoenzymes can provide diagnostically useful organ-related information.

1.11.1 Indication

1.11.2 Method of determination

IFCC Primary Reference Procedure for the Measurement of Catalytic Activity Concentration of Lactate Dehydrogenase at 37 °C /1/

Principle: The LD activity is measured at a pH of 9.4 as the amount of lactate consumed, by continuous monitoring the increase in absorbance due to the reduction of NAD+ at 339 (Hg 334 or Hg 365). The equilibrium is far on the side of lactate and NADH (Tab. 1.11-2 – Principles of LD determination).

Selective determination of LD-1

Chemical inhibition of isoenzymes containing the M subunit

Principle: 1,6-hexanediol or sodium perchlorate are added to the reaction medium as selective inhibitors of the LD isoenzymes with M subunits so that only the LD-1 that has four H subunits is measured /2/.

Immunological inhibition of isoenzymes containing the M subunit

Principle: Antibodies against the M subunit are added to the sample and form immune complexes with isoenzymes possessing this subunit. The immune complexes are removed by centrifugation and LD-1 is determined in the supernatant /3/.

Differentiation of isoenzymes by electrophoresis

Principle: the serum is fractionated by electrophoresis on agarose gel or on cellulose acetate strips at an alkaline pH. The rate of migration to the anode depends on the subunit composition of the isoenzyme. Isoenzymes with the subunit H migrate quickly, those containing the subunit M migrate slowly; thus, LD-1 has the highest migration rate toward the anode and LD-5 the lowest. In agarose gel electrophoresis LD-5 migrates toward the cathode.

The isoenzyme fractions are visualized in cellulose acetate electrophoresis by coupling the enzymatically formed pyruvate with a tetrazolium salt /4/.

In agarose gel electrophoresis, the separation lane is covered with an overlay containing lactate and NAD+ and, after incubation at 37 °C, the fluorescence of NADH is measured at 410 nm, under excitation at 365 nm /2/.

1.11.3 Specimen

Serum, plasma, effusion fluid: 1 mL

1.11.4 Reference interval

See Tab. 1.11-3 – LD reference intervals.

1.11.5 Clinical significance

The LD is a cytoplasmic enzyme and present in all tissues. Leakage into the plasma can occur even after minor tissue damage, and levels are elevated in many pathological conditions. Diseases associated with increases in LD activity are shown in Tab. 1.11-4 – Diseases that may cause elevated LD in serum. The LD is diagnostically as unspecific as the erythrocyte sedimentation rate. Hence, it is of limited significance and should mainly be used /8/:

Important diagnostic indicators for tissue-specific differentiation of elevated LD levels are:

LD/AST ratio

The ratio is used to differentiate between prehepatic, hemolysis-induced or dyserythropoiesis-induced jaundice from hepatic jaundice (Fig. 1.11-1 – Differentiation between prehepatic and hepatic jaundice). Ratios above 5 are indicative of hemolytic jaundice lower values point to the hepatic form. Ratios above 5 can also occur in metastatic liver disease and infectious mononucleosis. In prehepatic jaundice, except in severe hemolytic crises (sickle-cell anemia), the bilirubin concentration is below 6 mg/dL (100 μmol/L) /10/.

Quantitative analysis of LD isoenzymes

The LD molecule consists of four polypeptide chains of the two types M and H, both of which are under separate genetic control. The five isoenzymes listed in Tab. 1.11-1 – Isoenzymes of LD are distinguished by the basis of their subunit composition. The assessment by electrophoresis distinguishes three LD patterns (Tab. 1.11-5 – Differential diagnostic information of electrophoretic LD patterns/4/:

1.11.6 Comments and problems

Sample processing

Plasma should be centrifuged at high speed (10 min. at 3,000 × g) because otherwise it will still contain platelets; these have a high LD concentration.

Reference interval

If the blood sample is collected after physical exertion (muscle activity), the LD levels can be higher than the upper reference limit. Capillary serum and plasma have higher LD levels. The levels in serum are higher than those in plasma due to hemolysis during the coagulation process.

Hemolysis

Hemolysis causes increased LD levels because the LD concentration in erythrocytes is 360-fold higher than in plasma. At a mean activity of 165 U/L, hemolysis of 0.8 g Hb/L causes an increase in LD by 58% /38/. The serum must have separated from the clot within 2 hours.

Platelet interference

Serum and platelet-free plasma have the same LD activity. The interference caused by platelet contamination in the LD activity of a plasma sample depends on the reaction conditions. If the sample is pipetted into a relatively large volume of hypotonic reagent, lysis will result in elevated LD levels. If the sample is added to an isotonic reagent, lysis will not occur, but optical interference will result. Falsely low LD levels are measured because the NADH-related absorbance during the LD reaction is masked by an increase in the absorbance caused by light absorption by the platelets /39/.

A stronger platelet contamination of heparin anticoagulated blood due to inadequate centrifugation only results in slightly increased imprecision in the IFCC method /40/.

Stability

LD in serum is stable for up to 7 days at room temperature (20 °C) /2/. For routine analysis, the serum should be stored at room temperature due to the instability of LD-4 and LD-5 under cold conditions.

Drugs

In vivo-elevations of the LD levels can be caused by allopurinol, amiodarone, androgenic/anabolic steroids, aspirin/salicylates, captopril, carbamazepine, chlorpromazine, cisplatin, clozapine, cumarin, dacarbazine, diltiazem, erythromycin, fluphenazine, gold salts, α-methyldopa, naproxen, paracetamol, papaverine, penicillamine, perhexillin, phenytoin, phenylbutazone, propylthiouracil, ranitidine, sulfasalazine, tienilic acid, valproate acid, verapamil /41/.

Half-life

LD-1, 4–5 days, LD-5, 10 hours.

Macro LD

For further information, see Tab. 1.1-2 – Macroenzymes: characterization, clinical significance and laboratory findings.

1.11.7 Pathophysiology

LD is a hydrogen-transferring enzyme that catalyzes the oxidation of L-lactate to pyruvate using the coenzyme NAD+ as a hydrogen acceptor. The reaction is reversible. The reduction of pyruvate to lactate is strongly promoted under physiological pH conditions.

Each LD molecule consists of 4 subunits with a molecular weight of 34 kDa. There are two types of subunits, the heart (H) type and the muscle (M) type, that are encoded by different gene loci. The H and M types are combined in the tissues to form five isoenzymes (LD-1–5). The H type is predominant in tissues with high O2 consumption, while the M type is predominant in tissues with high glycolytic activity.

The LD is present in all somatic cells. It is dissolved in the cytoplasm and released in the event of cell damage. The enzyme activity differs in the individual tissues and is 147 U/g in skeletal muscle, 124 U/g in myocardium, 145 U/g in the liver and 106 U/g in the kidney. Erythrocytes contain 31 U/g of hemoglobin. The activity in the tissues is on average 500-fold higher than in serum, and even minor tissue injury can cause elevated LD levels. In addition, many tissues have a different isoenzyme inventory. LD-1 and LD-2 are predominant in the myocardium and erythrocytes, and LD-5 is predominant in the liver. LD-3 and LD-4 are present in the lung, lymphatic system, spleen, endocrine glands and platelets.

In diseases, the LD activity is dependent on the isoenzymes entering the plasma from the tissues, the elimination rate of the isoenzymes and their subunits. The half-life of the liver-specific LD-5 (M4) is 8–12 hours which is only about 1/10 of that of the heart-specific and erythrocyte-specific LD-1 (H4). Therefore, in many cases, a liver-specific LD enzyme pattern is only measured for a short time, while an enzyme pattern due to myocardial injury or hemolysis is measured for a longer time /11/.

The LD detectable in serum in progressive Duchenne muscular dystrophy mainly corresponds to the isoenzymes LD-1–3 and not to the LD-4 of the healthy skeletal muscle. Since this abnormality is also found in the carriers, these are thought to be genetically unable to form sufficient amounts of the M subunit /19/.

Concomitant hepatitis in infectious mononucleosis (IM) can be distinguished from the other viral hepatitides by the high activity of the LD in relation to the aminotransferases. It is not the hepatic isoenzyme LD-5 that is pathologically elevated, but LD-3 and LD-4 that originate from lymphoid cells.

Elevated LD levels in megaloblastic anemia are caused by ineffective erythropoiesis because red cell precursors do not mature in the medulla due to vitamin B12 or folic acid deficiency and are subject to apoptosis.

References

1. IFCC Primary Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes at 37 °C. Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase. Clin Chem Lab Med 2002; 40: 643–8.

2. Henderson AR. Isoenzymes of lactate dehydrogenase. In: Bergmeyer HU, ed. Methods of enzymatic analysis, 3rd edition, vol 3. Weinheim; Verlag Chemie 1983: 138–55.

3. Usategui-Gomez M, Wicks RW, Warshaw M. Immunochemical determination of the heart isoenzyme of lactate dehydrogenase (LDH1) in human serum. Clin Chem 1979; 25: 729–34.S

4. di Giorgio J. Determination of serum lactic dehydrogenase isoenzymes by the use of diagnostic test cellulose acetate electrophoresis system. Clin Chem 1971; 17: 326–31.

5. Schumann G, Klauke R. New IFCC reference procedures for the determination of catalytic activity concentrations of five enzymes in serum: preliminary upper reference limits obtained in hospitalized patients. Clin Chim Acta 2003; 327; 69–79.

6. Thomas L, Müller M, Schumann G, Weidemann G, Klein G, Lunau S, Pick KH, Sonntag O. Consensus of DGKL and VDGH for interim reference intervals on enzymes in serum. J Lab Med 2005; 29: 301–8.

7. Heiduk M, Päge I, Kliem C, Abicht K, Klein G. Pediatric reference intervals determined in ambulatory and hospitalized children and juveniles. Clin Chim Acta 2009; 406:156–61.

8. Huijgen H, Sanders GTB, Koster RW, Vreeken J, Bossuyt PMM. The clinical value of lactate dehydrogenase in serum: a quantitative review. Eur J Clin Chem Clin Biochem 1997; 35: 569–79.

9. Zimmerman HJ, Maddrey WC. Acetaminophen (paracetamol) hepatotoxicity with regular intake of alcohol: analysis and instances of therapeutic misadventure. Hepatology 1995; 22: 767–73.

10. Helzberg JH, Spiro HM. “LFTs” test more than liver. J Am Med Assoc 1986; 256: 3006–7.

11. Schmidt E, Schmidt FW. Diagnostik des Ikterus. Dtsch Med Wschr 1984; 109: 139–46.

12. Werner M, Brooks SH, Mohrbacher RJ, Wasserman AG. Diagnostic performance of enzymes in the determination of myocardial infarction. Clin Chem 1982; 28:1297–302.

13. Shahangian S, Ash KO, Wahlstrom NO, et al. Creatinkinase and LDH-isoenzymes in serum of patients suffering burns, blunt trauma, or myocardial infarction. Clin Chem 1984; 30: 1332–8.

14. Carstens V, Büscher J, Niehues B, Behrenbeck DW. Die intravasale Hämolyse bei neueren Herzklappenprothesen. Herz-Kreislauf 1981; 6: 261–5.

15. Meissner E, Fabel H. Akute Lungenembolie. Arzneimitteltherapie 1990; 8: 177–92.

16. Schmidt E, Schmidt FW. Enzyme diagnosis of diseases of the liver and the biliary system. In: Schmidt E, Schmidt FW, Trautschold I, Friedel R, eds. Advances in clinical enzymology. Basel; Karger 1979: 239–92.

17. Rotenberg DH, Weinberger I, Davidson E, et al. Total lactate dehydrogenase and its isoenzymes in serum of patients with infectious mononucleosis. Clin Chem 1991; 37: 116–7.

18. Castaldo G, Oriani G, Cimino L, Topa M, Budillon G, Salvatore F, et al. Serum lactate dehydrogenase isoenzyme 4/5 ratio discriminates between hepatocarcinoma and secondary liver neoplasia. Clin Chem 1991; 37: 1419–23.

19. Laudahn G, Heyck H, Feustel F. Enzyme im Serum bei Muskelkrankheiten. In: Praktische Enzymologie. Bern: Huber, 1968: 249.

20. Kazmierczak SC, Castellani WJ, von Lente F, Hodges ED, Udis B. Effect of reticulocytosis on LDH isoenzyme distribution in serum: in vivo and in vitro studies. Clin Chem 1990; 36: 1638–41.

21. Vilpo JA, Talvensaari KK, Mortensen E. Hemolysis: which laboratory investigation and when? Scand J Clin Lab Invest 1990; 50: 10–9.

22. Winston RM, Warburton FG, Stott A. Enzymatic diagnosis of megaloblastic anemia. Br J Hematol 1970; 19: 587–92.

23. Patton JF, Manning KR, Case D, Owen J. Serum lactate dehydrogenase and platelet count predict survival in thrombotic thrombocytopenic purpura. Am J Hematol 1994; 47: 94–9.

24. Carcamo C, Pallares E, Rubi J, et al. Lactate dehydrogenase isoenzymes in patients with essential thrombocythemia. Thrombos Res 1993; 70: 111–6.

25. Domanovits H, Paulis M, Nikfardjam M, Meron G, Kürkciyan I, Bankier AA, Laggner A. Acute renal infarction. Medicine 1999; 78: 386–94.

26. Kang SK, Ha CY, Cho KH, Park SK, Kim UH. Changes of lactate dehydrogenase and its isoenzyme activity in renal diseases. Nephron 1991; 57: 55–9.

27. Maiche AG, Muhonen T, Porkka K. Lactate dehydrogenase changes during granulocyte colony-stimulating factor treatment. Lancet 1992; 340: 853.

28. Krafft J, Fink R, Rosalski SB. Serum enzymes and isoenzymes after surgery. Ann Clin Biochem 1977; 14: 294–6.

29. Shuster J, Williams NB, Castleberg R, et al. Serum lactate dehydrogenase in childhood neuroblastoma. Am J Clin Oncol 1992; 15: 295–303.

30. Dimopoulos MA, Barlogie B, Smith TL, Alexanian R. High serum lactate dehydrogenase level as a marker for drug resistance and short survival in multiple myeloma. Ann Int Med 1991; 115: 931–5.

31. Bien E, Balcerska A. Serum soluble interleukin-2 receptor, beta2-microglobulin, lactate dehydrogenase and erythrocyte sedimentation rate in children with Hodgkin’s lymphoma. Clin Immunol 2009; 70: 490–500.

32. van Eyben FE, Blaabjerg O, Hyltoft-Petersen P, Lindegaard Madsen E, Amato R, Liu F, Fritsche H. Lactate dehydrogenase isoenzyme 1 and prediction of death in patients with metastatic germ cell tumors. Clin Chem Lab Med 2001; 39: 38–41.

33. Bolwell B, Pohlmann B, Kakaycio M, Wise K, Goormastic M, Andresen S. LDH elevation after autologous stem cell transplantation. Bone Marrow Transplantation 1999; 24: 53–5.

34. Montesinos P, Lorenzo I, Martin G, Sanz J, Perezirvent M, Martinez D, et al. Tumor lysis syndrome in patients with acute myeloid leukemia: identification of risk factors and development of a predictive model. Haematologica 2008; 93: 67–74.

35. van Krugten MV, Cobben NAM, Lamers RJS, van Dieijen-Visser MP, Wagenaar SJ, Wouters EFM, Drent M. Serum LDH: a marker of disease activity and its response to therapy in idiopathic pulmonary fibrosis. Netherlands J Med 1996; 48: 220–3.

36. Lassen U, Osterlind K, Hansen M, Dombernovsky P, Bergner B, Hansen HH. Long-term survival in small-cell lung cancer posttreatment characteristics in patients surviving 5–10 years – an analysis of 1.714 consecutive patients. J Clin Oncol 1995; 13: 1215–20.

37. Sattler FR, Walzer PD. Pneumocystis carinii. Baillière’s Infectious Diseases 1995; 2: 471–85.

38. Sonntag O. Haemolysis as an interference factor in clinical chemistry. Clin Chem Clin Biochem 1986; 24: 127–39.

39. Paeke MJ, Pejakovic M, Alderman MJ, Penberthy LA, Walmsley RN. Mechanism of platelet interference with measurement of lactate dehydrogenase activity in plasma. Clin Chem 1984; 30: 518–20.

40. Herzum I, Bünder R, Renz H, Wahl HG. Reliability of IFCC method for lactate dehydogenase measurement in lithium-heparin plasma. Clin Chem 2003; 49: 2094–6.

41. Salway JG. Drug interaction handbook. London: Chapman and Hall Medical, 1990.

1.12 Lipase

Klaus Lorentz

Lipase measured in serum is synthesized in the acinar cells of the pancreas and stored in their granules. More than 99% is secreted into the pancreatic duct system via the apical pole of the cells. In acute pancreatitis, the enzyme is increasingly released into the blood due to increased permeability at the basal cell pole of lipase secreting cells.

1.12.1 Indication

1.12.2 Method of determination

The hydrolysis of triglycerides, diglycerides and mono glycerides is the basic reaction of any determination. In the titrimetric method, the release of fatty acid at the C atom 1 or 3 of glycerol is measured. Multistage photometric methods are based on the determination of glycerol following the enzymatic cleavage of remaining acyl residues. A single-step photometric procedure uses a triglyceride analog as a substrate /1/. The analytical specificity of all methods is limited because substrates that are soluble even in the presence of bile acids or detergent-dissolved substrates allow degradation by esterases.

Auto titration /2/: this method has the highest analytical specificity. During enzymatic hydrolysis, oleic acid released from a triolein or olive oil emulsion is continuously titrated with alkaline solution to pH 9.0 (pH-stat). Since a proton is neutralized with each cleaved ester bond, this method allows direct measurement, but is not suited for routine analysis due to its technical requirements. It is well standardized; all photometric methods refer to auto titration /23/.

Turbidimetric assay /4/: the conditions are similar to those of auto titration; however, the increase in lipase after addition of heparin indicates a co-reaction of lipoprotein lipase. Measurement is performed by photometry near 550 nm referring to lipase standards calibrated by titrimetry. The start and duration of the measurement intervals are selected by analyzers such that temporal linear reaction rates are to be assumed and measuring ranges of 5–10-fold the upper reference limit are reached. There is the analytical shortcoming of positive interference by esterases, although all methods use esterases in their assay medium.

DGMRE method /1/: this is a single-step procedure that uses the substrate 1,2-dilauryl-rac-glycero-3-glutaric acid-(6-methylresorufin)-ester (DGMRE) as triglyceride analog. Two esters in this triglyceride analog are replaced by hydrolysis-resistant ether. Therefore, lipase cleaves an acromatic acyl residue only at C atom 1. The residue spontaneously decomposes into glutaric acid and red methylresorufin.

Diglyceride method /4/: in this color assay, lipase releases a 2-mono glyceride from a 1,2-diglyceride; the 2-mono glyceride is degraded to glycerol by mono glyceride lipase. After another three reactions (phosphorylation, oxidation, oxidative coupling), the glycerol is measured as benzochinonediimine dye. Besides lipoprotein lipase and cholesterol esterase, intestinal lipase and carboxyl esterase are also thought to react.

Multilayer film slide test (Vitros method) /5/: this method uses 1-oleoyl-2,3-diacetylglycerol as a substrate. Lipase cleaves it to oileic acid and 2,3-diacetylglycerol, from which glycerol is released through diacetinase and, after the reaction chain described above, measured as dye. Since dodecylbenzene sulfonate replaces bile acid as solubilizer, there is glycerol interference /6/ as well as interference from all enzymes mentioned /7/ so that the method is preferably applied for measuring gastrointestinal lipases /8/.

1.12.3 Specimen

1.12.4 Reference interval

Refer to Tab. 1.12-1 – Lipase reference intervals.

1.12.5 Clinical significance

The diagnostic assessment of the lipase activity in serum is dependent on the selected method and the clinical requirement. All methods are qualified for the monitoring of acute or chronic recurrent pancreatitis without involvement of other abdominal organs; only assays employing a triglyceride emulsion are suited for excluding these diseases.

The following rules should generally be adhered to when serum lipase activity is assessed:

In contrast to the α-amylase, occasional subnormal lipase levels can be measured with the immunological assay /2/ in excretory pancreatic insufficiency /15/. In the course of pancreatic inflammations and following endoscopic retrograde choledochopancreatography (ERCP), lipase behaves like α-amylase and its non-salivary fraction. The original assumption of different lipase/α-amylase ratios in alcohol-induced and bile-induced pancreatitides did not stand critical verification. The detection of isolipases with the multi layer film slide test also did not find its way into clinical diagnostics because, compared to isoamylases, the significance of these (possible) isoenzymes is largely unknown.

Hyperlipasemias cause diagnostic problems in chronic inflammatory bowel diseases. Elevated α-amylase or lipase levels do not necessarily indicate pancreas involvement or pancreas injury by azathioprine and sulfasalazine /16/.

Hyperenzymemia is found in 14–21% of Crohn’s disease and ulcerative colitis, where lipase leaves the reference interval more often than α-amylase even in the absence of pancreatitis /17/.

Pancreatic carcinomas only cause hyperenzymemia (by occlusion of the pancreatic duct) in rare cases, while normal α-amylase but significantly elevated lipase levels are observed in undifferentiated malignoma and hepatocellular carcinomas and adenocarcinomas without autoptical evidence of pancreas involvement /18/. Lipase levels up to 20-fold the upper reference limit immunologically measured in cases of diabetic ketoacidosis are positively pancreatogenic. They occur in 50% of the patients with an increase in trypsin and α-amylase, but without clinical symptoms of pancreatitis /19/. The diseases associated with increased activity of lipase are shown in Tab. 1.12-3 – Causes of elevated lipase in serum.

1.12.6 Comments and problems

Anticoagulants

Due to complexing of Ca2+, the sample must not contain EDTA, oxalate, fluoride or citrate.

Method of determination

Except in the multi layer film slide test, sera with triglyceridemia above 870 mg/dL (10 mmol/L) should be diluted. Hemoglobin above 5 g/L and bilirubin above 47 mg/dL (800 μmol/L) decrease the measured values. Drugs in normal doses have no influence.

Using the assay with 1,2-diglyceride on random access analyzers carry-over of esterase from the cholesterol reagent into the reaction mixture has to be avoided. Glycerol interferes with the multi layer film slide test.

Macrolipasemia

See Tab. 1.1-2 – Macroenzymes.

Stability

In serum at least 1 week at 4 °C or 25 °C or 1 year at –28 °C.

1.12.7 Pathophysiology

Human pancreatic lipase (triacylglycerol acyl hydrolase, EC 3.1.1.3) is a monomeric glycoprotein of 449 amino acids in two domains with a molecular weight of 47 kDa. Typically, it only hydrolyzes insoluble triglyceride esters of long-chain fatty acids at the water-substrate interface at pH 8.8–9.2 if the substrate includes bile acids in micellar complexes. Colipase (molecular weight 9.9 kDa) activates the catalytic center by opening an overlying lid of 12 amino acids, anchors it to the hydrophobic boundary and protects the enzyme against inactivation by bile acids.

Lipase is produced in the acinar cells of the pancreas and more than 99% is released to the duct system of the gland via the apical cell pole. Less than 1% enters the lymph and blood capillaries at the basal pole (exogenous/endogenous partition) resulting in a concentration gradient of 1 : 500 to 1 : 800 between serum and duodenal secretion.

In acute pancreatitis, the basal cell pole shows abnormal permeability associated with increased entry of the enzyme into the circulatory system. In addition, cell necrosis occurs in the hemorrhagic form. If normal drainage is impaired, for example by scar strictures in chronic inflammation, sialolithiasis, obstruction due to papillary tumor or papilledema, the secretion pressure causes isthmic dehiscences and drainage into pericapillary spaces.

In chronic pancreatitis, this process is associated with further parenchymal atrophy that is not detected by decreased lipase activity in serum because of the small endogenous enzyme fraction. On the contrary, the activity in serum rises on recurrence, as in acute inflammation of chronic pancreatitis, associated with pain due to impaired drainage of the congested organ. Therefore, functional insufficiency cannot be detected by lipase determination in serum, not even after secretin-pancreozymin stimulation, but only by measuring the intraduodenal effect of lipase.

The lipase level rises with increasing age. The activity measured in the serum of the umbilical cord is only 12% of that present between 3–50 years of age and increasing to 112% until 70 years of age /2/. The enzyme has a half-life of 6.9–13.7 hours. It undergoes glomerular filtration with a clearance of 6 mL/min, complete tubular re-absorption and is degraded so that lipase is detectable in urine only in pronounced proteinuria.

References

1. Neumann U, Junius M, Batz HG. New substrates for the optical determination of lipase. European patent 207252 (1987).

2. Tietz NW, Astles JR, Shuey DF. Lipase activity measured in serum by a continuous-monitoring pH-stat technique – an update. Clin Chem 1989; 35: 1688–93.

3. Ziegenhorn J, Neumann U, Knitsch KW, Zwez W. Determination of serum lipase. Clin Chem 1979: 25: 1067.

4. Imamura S, Misaki H. An enzymatic method using 1,2-diglyceride for pancreatic lipase test in serum. Clin Chem 1989; 35: 1126.

5. Mauck JC, Weaver MS, Stanton C. Development of a Kodak Ektachem clinical chemistry slide for serum lipase. Clin Chem 1984; 30: 1058–9.

6. Bilodeau L, Grotte DA, Preese LM, Apple FS. Glycerol interference in the serum lipase assay falsely indicates pancreas injury. Gastroenterology 1992; 103: 1066–7.

7. Demanet C, Goedhuys W. Haentjens M, Huyghens L, Blaton V, Gorus F. Two automated fully enzymatic assays for lipase activity in serum compared: positive interference from post-heparin lipase activity. Clin Chem 1992; 38: 288–92.

8. Kazmierczak SC, van Lente F. Effect of gastric lipase on turbidimetric and dry-film methods for measuring pancreatic lipase. Clin Chem 1992; 38: 2555–6.

9. Junge W, Abicht K, Goldman J, Luthe H, Niederau C, Parker J, Watanabe S, Prinzing U, Klein G. Multicentric evaluation of the colorimetric liquid assay for pancreatic lipase on Hitachi analyzers. Clin Chem Lab Med 1999; 37, Special Suppl: 469.

10. Fossati P, Ponti M, Paris P, Berti G, Tarenghi G. Kinetic colorimetric assay of lipase in serum. Clin Chem 1992; 38: 211–5.

11. Panteghini M, Pagani F, Bonora R. Clinical and analytical evaluation of a continuous enzymatic method for measuring pancreatic lipase activity. Clin Chem 1993; 39: 304–8.

12. Abicht K, Heiduk M, Körn S, Klein G. Lipase, p-amylase, CRP-hs, and creatinine: Reference intervals from infancy to childhood. Abstract European Congress of Clinical Chemistry and Laboratory Medicine. Barcelona 2003.

13. Tietz NW, Shuey DF. Lipase in serum – an elusive enzyme: an overview. Clin Chem 1993; 39: 746–56.

14. Soldin SJ, Brugnara C, Wong EC. Pediatric reference ranges. Washington DC; AACC Press 2003: 135.

15. Weiß T, Lorentz K. Vergleichende Lipasebestimmung mit turbidimetrischer Technik und Enzymimmunoassay. Lab Med 1984; 8: 63–7.

16. Katz S, Bank S, Greenberg RE, Lendvai S, Lesser M, Napolitano B. Hyperamylasemia in inflammatory bowel disease. J Clin Gastroenterol 1988; 10: 627–30.

17. Bokemeyer B. Asymptomatic elevation of serum lipase and amylase in conjunction with Crohn’s disease and ulcerative colitis. Z Gastroenterol 2002; 40: 5–10.

18. Møller-Petersen J, Andersen PT, Hjorne N, Ditzel J. Hyperamylasemia, specific pancreatic enzymes, and hypoxanthine during recovery from diabetic ketoacidosis. Clin Chem 1985; 31: 2001–4.

19. Müller-Hansen J, Müller-Plathe O, Pröpper H. Untersuchungen zur diagnostischen Sensitivität von Lipase- und Amylase-Bestimmungen. Einfluss der ERCP auf die Aktivität von Serum-Lipase und Amylase. Ärztl Lab 1986; 32: 17–23.

1.13 Acid phosphatase (ACP)

Lothar Thomas

1.13.1 Indication

1.13.2 Method of determination /1/

Principle: Hydrolysis of 4-nitro phenyl phosphate by acid phosphatase at pH 4.9 liberates 4-nitro phenol. The reaction is stopped by raising the pH to 11 by addition of NaOH. At this pH the strongly-colored quinonoid 4-nitro phenolate ion is produced and its absorbance measured at 405 nm.

In the method modified by Hillmann enzymatic hydrolysis of 1-naphthyl phosphate at pH 5.6 liberates 1-naphthol. At this pH, 1-naphthol combines rapidly with the stabilized diazonium salt, Fast Red TR, present in the incubation mixture to form a red dye. The appearance of the dye is monitored continuously at 410 nm.

1.13.3 Specimen

Serum, plasma (no heparin and oxalate): 1 mL

1.13.4 Reference interval

Refer to Tab. 1.13-1 – Reference interval of acid phosphatase.

1.13.5 Clinical significance

The term acid phosphatase summarizes all phosphatases with their maximum enzymatic activity at a pH below 7.0. Accordingly, the ACP (EC 3.1.3.2) detectable in serum is a mixture of numerous enzymes predominantly coming from thrombocytes,erythrocytes, bones, cells of the reticuloendothelial system and the prostate. Activities from the prostate and thrombocytes, in particular, are tartrate-inhibitable. Elevated ACP levels can be indicators of prostate carcinoma, diseases of the skeletal system and the reticuloendothelial system (Tab. 1.13-2 – Diseases possibly associated with elevated ACP in serum).

References

1. Hillmann G. Fortlaufende photometrische Messung der sauren Prostataphosphataseaktivität. Z Klin Chem Klin Biochem 1971; 9: 273–4.

2. Andersch MA, Srzcypinski AJ. Use of p-nitrophenylphosphate as the substrate in the determination of serum acid phosphatase. J Clin Pathol 1947; 17: 571–4.

3. Kraus E, Sitzmann FC. Die saure Phosphatase im Serum bei Kindern. Pädiatr Prax 1973; 12: 321–6.

4. Seiler D, Nagel D, Tritschler W, Looser S. Saure Phosphatase im Serum (Substrat: α-Naphthylphosphat): Referenzwerte und diagnostische Aussage. J Clin Chem Clin Biochem 1983; 21: 519–25.

5. Pearson JC, Dombrovskis S, Dreyer J, et al. Radioimmunoassay of serum prostatic acid phosphatase after prostatic massage. Urology 1983; 21: 37–40.

6. Van Lente F. Alkaline and acid phosphatase determinations in bone disease. Orthoped Clin North Am 1979; 10: 437–50.

7. Mercer DW, Peters SP, Glew RH, Lee RE, Wenger DM. Acid phosphatase isoenzyme in Gaucher’s disease. Clin Chem 1977; 23: 631–5.

Table 1.1-1 Half-lives of serum enzymes

Enzyme

Half-life

ALP

3–7 days

α-amylase

9–18 hours

ALT (GPT)

50 hours

AST (GOT)

12–14 hours

CHE

10 days

CK

12 hours

CK-MM

20 hours

CK-MB

10 hours

CK-BB

3 hours

GLD

14–18 hours

GGT

3–4 days

LD-1

4–5 days

LD-5

10 hours

Lipase

7–14 hours

GGT, gamma-glutamyl transferase

Table 1.1-2 Macroenzymes: characterization, clinical significance and laboratory findings /610/

Clinical and laboratory findings

Alkaline phosphatase (ALP) /9/

The macro ALP can be detected in serum as an immunoglobulin-bound macroenzyme or as an macroenzyme bound to other molecules.

Immunoglobulin-bound form: This form is complexed with one of the three immunoglobulin classes, and mostly with IgG. The antibodies only react with specific isoenzymes existing in two antigenic groups: antigenic determinants of the placenta/intestine group or the liver/bone group. The antibodies can react with two isoenzymes of the same antigenic group, but not with two isoenzymes of different antigenic groups. The complexes include liver ALP, bone ALP or intestinal ALP. In terms of electrophoresis, the macro ALP travels very slowly and can be detected in immunoelectrophoresis using anti-human serum. The detection of immunoglobulin-bound macro ALP has no clinical significance.

Macro ALP bound to other molecules: Macro ALP is also known as “particulate ALP". The molecular weight is about 1000 kDa. The ALP is bound to membrane fragments or lipoprotein X. This macro ALP is often detected in liver diseases.

α-amylase /11/

Macroamylase is one of the most often detected macroenzymes, with an incidence of 0.98% in patients with normal α-amylase activity and 2.56% in patients with elevated activity. The α-amylase can be detected in serum as an immunoglobulin-bound macroenzyme or as an macroenzyme bound to other molecules.

Immunoglobulin-bound form: this form is complexed with IgG or IgA; both pancreatic and salivary gland amylase can be involved. Normal α-amylase has a molecular weight of 55 kDa whereas that of macroamylase is approximately 210 kDa. Therefore, macroamylase does not undergo glomerular filtration and accumulates in the plasma. In agarose gel electrophoresis, the immunoglobulin-bound form mostly presents as blurred fraction superimposed on the salivary gland amylase that is cathodically positioned in relation to the pancreatic amylase. Detection by way of gel filtration based on Bio-Gel 100 is to be preferred. In standard enzyme analysis, macroamylase cannot be distinguished from normal α-amylase. The detection of immunoglobulin-bound macroamylase has no clinical significance.

Macroamylase bound to other molecules: this form is iatrogenic and based on the infusion of high-molecular-weight glycoproteins such as hydroxy ethyl starch (HAES) that forms a high-molecular-weight complex with the α-amylase. This form of macroamylasemia is of transient nature and lasts 3–5 days after infusion of HAES because the α-amylase does not undergo glomerular filtration until the HAES has been broken down.

Indications of macroamylasemia: elevated serum amylase at normal lipase. Macroamylasemia is likely if the lipase in serum is within the reference interval. An α-amylase creatinine clearance ratio below 1% is also indicative of macroamylasemia.

Aminotransferases (AST, ALT) /1213/

Macro complexes of AST and immunoglobulin, especially IgG, are much more common than immune complexes of ALT and IgG. However, macroenzymes of aminotransferases are generally less common than macroamylase and macro CK. The macro forms of aminotransferases are less common in children and adolescents than in adults. The AST occurs in two forms: the cytosolic AST (cAST) and the mitochondrial AST (mAST). The cAST is complex-bound more often than mAST. Patients with cAST bound to IgG and mAST bound to IgA have also been described. AST-IgA complexes have been described in patients with liver diseases. In a study /14/ on patients with AST-IgA complexes, the proportion of such detected complexes was 41.8% in chronic hepatitis, 62.2% in liver cirrhosis, 90% in hepatocellular carcinoma and 66.7% in alcoholic liver disease.

Laboratory findings: the detection of macro AST and macro ALT can be performed by differential precipitation with polyethylene glycol, by electrophoresis, by gel filtration or by removing immunoglobulin from the serum with protein A or protein G. In a study /15/ on 44 clinically normal children, 17 individuals had macro AST and AST activities of 50–1150 U/L. The detection was performed by precipitation with 24% polyethylene glycol 6000 and determination of AST in the supernatant. The proportion of AST (% PPA) in the precipitant was determined. In cases of PPA above 75%, the diagnostic sensitivity for macro AST was 82.4% at 88.9% diagnostic specificity.

Creatine kinase (CK) /16/

Macro CK in serum occurs in two forms: the immunoglobulin-associated form (type 1) and other forms, for example, oligomeric (type 2). Prevalence is 0.3 to 1%.

Macro CK type 1: type 1 consists of a complex constituted of an immunoglobulin (usually IgG or IgA) bound to two CK molecules (usually CK-BB isoenzymes). It persists for months or years. The macro CK type 1 frequently causes increased total CK activity and is detected in patients with various diseases and also in seemingly healthy individuals. Macro CK type 1 usually affects individuals over 50 years of age and is more common in women than in men. Autoimmune disorders, cardiovascular symptoms and life-threatening conditions have often been described. Inexplicable disproportionate elevations are measured during enzymatic determination of CK-MB activity in immune inhibition assays. This is because no immune inhibition can take place with macro CK since macro CK has no CK-M subunit. Therefore, the result after multiplication by 2 shows seemingly higher CK-MB activity than total CK activity. The detection of macro CK type 1 is performed in immune inhibition assays, by gel chromatography or based on the percentage of the polyethylene glycol-precipitable activity (% PPA), upper reference limit: 45% /17/.

Macro CK type 2: Type 2 is a polymer of the mitochondrial CK. It is detected in up to 3.7% of hospitalized patients. The mitochondrial CK is not structurally related with the M subunit and B subunit of the CK. It is encoded by a separate gene. The molecular weight of macro CK type 2 is more than 300 kDa. Macro CK type 2 originates from the liver and is released as a result of cell necrosis and in critically ill patients. It can also be elevated in the serum in such cases. As a rule, the total CK is normal or only mildly elevated.

Laboratory findings /17/: In a study, 30 in 255 requests for macro CK were positive (28 type 1 and 2 type 2). The median CK elevation was 731 (249–1238) U/L in women and 356 (241–462) U/L in men. Over 80% of patients with macro CK type 1 were women.

Gamma-glutamyl transferase (GGT) /1819/

The GGT in serum occurs in three molecular forms with molecular weights > 1 million kDa, 250 to 500 kDa and 120 kDa, respectively. The latter is the free hydrophilic form of the enzyme resulting from dissociation of the hydrophobic component through proteases. The high-molecular-weight GGT consists of a complex of lipoprotein X and GGT, the medium-molecular-weight GGT consists of a HDL/GGT complex. The GGT can also form complexes with lipoproteins A and B and immunoglobulin (IgA). The GGT is elevated in most liver diseases. The proportion of high-molecular-weight GGT is higher in obstructive liver injuries than in non-obstructive ones. It is also higher in extrahepatic obstruction than in intrahepatic obstruction. Thus, intrahepatic obstruction can be distinguished from extrahepatic obstruction by measuring the intermediate GGT with a diagnostic sensitivity of 88% at 96% specificity /18/. The molecular form of GGT can be determined by polyacrylamide gradient gel electrophoresis.

Lactate dehydrogenase (LD)

Macro LD is the third most common macroenzyme after α-amylase and CK. If present, it causes elevated LD in 89% of the cases /20/. Three macro forms are distinguished: Self-association of an LD isoenzyme, association with β-lipoprotein and association with an immunoglobulin. The latter form is most common. The autoantibodies a) react with the M subunit or – more rarely – with the H subunit and bind either LD 2–5 or LD 1–4, (b) react with the H or M subunit and bind LD 1–5 or (c) only react with the isoenzyme that includes both H and the M subunits. Group (c) comprises IgA-kappa antibodies that preferably react with LD-3 and less so with LD-2 and LD-4. In such cases, the immune response to LD is monoclonal. Hence, this form of macro LD occurs more often in lymphoproliferative diseases /21/. Macro LD increasingly occurs in inflammatory abdominal diseases, drug-induced hemolytic anemias and autoimmune disorders. Macro LD is detected by gel filtration on Sephadex G-200.

Lipase /2223/

Macro lipasemia is rare and caused by lipase binding to IgG or IgA autoantibodies. The molecular weight is approximately 200 kDa. Longer persisting macro lipase is detected in non-Hodgkin’s lymphoma, liver cirrhosis, inflammatory abdominal disease and also in association with macroamylasemia without acute or chronic active pancreatitis being present. Macro lipasemia results in increased lipase activity in serum only in some of the cases. Detection is performed by precipitation with polyethylene glycol or by gel filtration.

Table 1.1-3 Antibodies with regulating effects to the activity of tissue-specific enzymes /8/

Enzyme/inhibitor

Location and Disease association

Pyruvatedecarboxylase

Microsomes: Primary biliary cirrhosis

Thyroid peroxidase

Microsomes: autoimmune thyroid disorder

21-hydroxylase

Microsomes: Morbus Addison

Acetylcholinesterase

Cell membrane: myasthenia gravis

H+-K+-ATPase

Cell membrane: autoimmune gastritis

Glutamatedecarboxylase (GAD 65)

Cytosol: Type 1-diabetes

Glutamatedecarboxylase (GAD 67)

Cytosol: stiff-person syndrome, polyendocrine syndrome, type 2 with insulin-dependent diabetes

Carbonic anhydrase II

Cytosol: autoimmune cholangitis, endometriosis

Triosephosphate isomerase

Cytosol: hemolysis associated with Epstein-Barr virus infection or hepatitis A infection

Manganese superoxide dismutase

Cytosol: Epstein-Barr virus infection

Prostate-specific antigen

Cytosol: enign prostatic hyperplasia

Tissue plasminogen activator

Cytosol, blood: systemic lupus erythematosus

DNA helicase II (Ku antigen)

Nucleus: scleroderma, systemic lupus erythematosus

Topoisomerase (Scl 70)

Nucleus: scleroderma

Histidyl-tRNA synthase (Jo-1)

Nucleus: polymyositis, dermatomyositis

Alanyl-tRNA synthase (PL-12)

Nucleus: polymyositis

Threonyl-tRNA synthase (PL-7)

Nucleus: polymyositis

RNA polymerase I/II

Nucleus: scleroderma

Plasminogen activator inhibitor

Blood: systemic lupus erythematosus

Calpastin

Blood: rheumatoid arthritis

Table 1.1-4 Specific enzymes of important organs

Specific enzyme

Organ

Indication

α-amylase

Pancreas, salivary glands

Acute pancreatitis

Acute parotitis

ALT

Liver

Parenchymal injury

AST

Liver, muscle

Myocardial infarction, liver parenchymal disease, skeletal muscle disease

ALP

Liver, bones, intestines, kidneys

Skeletal injury, hepatobiliary disease

CK

Skeletal muscle, heart, non-striated muscle

Myocardial infarction, myopathy

Cholinesterase

Liver

Organophosphatic intoxication, liver injury

GLD

Liver

Severe liver parenchymal injury

GGT

Liver

Cholestatic disease, alcoholism

LD

Liver, heart, skeletal muscle, erythrocytes, thrombocytes, lymph nodes

Liver parenchymal injury, myocardial infarction, hemolysis, ineffective erythropoiesis, lymphomas

Lipase

Pancreas

Acute pancreatitis

Table 1.1-5 Differentiation of liver disease from other tissue damage

Quotient*

Indication

CK/AST

< 10

Myocardium

> 10

Skeletal muscle

LD/AST

> 12

Erythrocytes

* Applicable to enzyme measurement at 37 °C

Table 1.1-6 Enzyme pattern in acute severe tissue damage with cell necrosis

Tissue

Enzyme activity in serum/plasma

Liver parenchyma

LD > AST > ALT

Myocardium

CK > LD > AST >> ALT

Skeletal muscle

CK >> LD > AST >> ALT

Erythrocytes

LD >> AST > ALT

Symbols: > higher than the following enzyme, >> very much higher than the following enzyme.

Table 1.1-7 Enzyme pattern* in acute thoracic or abdominal pain, modified from Ref. /8/

Conjectural diagnosis

Enzyme pattern

Myocardial infarction

Moderate elevation of aminotransferase levels: CK > AST > ALT >> α-amylase >> GLD

Acute right heart failure

High elevation of aminotransferase levels: AST ~ ALT ~ GLD >> CK >> (α-amylase)

Pulmonary embolism

No to mild elevation of aminotransferase levels: ALT > AST > GLD > CK > (α-amylase)

Pleuritis

Usually no enzyme elevation

Abdominal vascular obstruction

Medium to high elevation of aminotransferase levels: AST ~ ALT > α-amylase > GLD > CK

Acute pancreatitis

Mild elevation of aminotransferase levels: Lipase > α-amylase >> ALT > AST ~ GLD >> CK

Biliary colic

Moderate elevation of aminotransferase levels: ALT > AST > GLD > α-amylase >> CK

Renal colic

Usually no enzyme elevation

Shock

Moderate to high elevation of aminotransferase levels: CK >> AST > ALT > GLD > α-amylase

* It is advisable to determine the enzyme pattern for CK, α-amylase or lipase, ALT (GPT), AST (GOT).

Transaminase elevation: mild, to approx. 3 times; moderate, 4–10 times; medium,11–20 times; high, more than 20 times the upper reference limit.

Explanation of symbols: ~ elevation by about the same factor; > higher elevation than the following enzyme; >> very much higher elevation than the following enzyme.

Table 1.1-8 Enzyme pattern in acute liver disease /24/

Disease in question

Enzyme pattern

Acute viral hepatitis

Pronounced elevation of aminotransferase levels: ALT > AST ~ LD >> GGT ~ ALP; AST/ALT ≤ 1,0

Acute liver necrosis (CCl4 intoxication, impaired blood flow)

Pronounced elevation of aminotransferase levels: LD > AST > ALT ~ GLD; AST/ALT > 2.0

Alcohol-toxic hepatitis

Moderate to medium elevation of aminotransferase levels: GGT > AST > ALT > ALP; AST/ALT > 1.0

Biliary tract obstruction

Medium elevation of aminotransferase levels: AST > ALT ~ LD ~ GGT > ALP; AST/ALT > 1.0

Liver cirrhosis

Mild elevation of aminotransferase levels: AST > ALT ~ GGT (post hepatitic cirrhosis); GGT >> AST (alcohol-toxic cirrhosis, biliary cirrhosis); AST/ALT > 2.0

Metastatic liver

Mild to moderate elevation of aminotransferase levels: ALP ~ GGT > AST > ALT; AST/ALT > 2.0

Table 1.1-9 Median peak value of 100 critically ill patients with no primary liver disease, but with bilirubin values > 3 mg/dL (51 µmol/L) /25/

Enzyme

CHE

LD

ALT

ALP

GGT

U/L*

1,500

1,300

130

200

200

* Values at 37 °C

Table 1.1-10 Incidence of elevated enzyme levels after abdominal surgery /27/

Enzyme

Incidence (%)

CK

76

AST

50

LD

44

LD-1

28

CK-MB

26

Table 1.1-11 Enzymes in malignant diseases /29/

Clinical and laboratory findings

Alkaline phosphatase (ALP)

Elevated ALP is diagnosed in cases of malignant tumors involving the liver or bones.

Bone involvement: ALP values measured in cases of osteosarcoma, parathyroid carcinoma and metastasized prostate carcinoma are up to 6 times the upper reference limit on average and only 2 times the upper reference limit in cases of multiple myeloma. Only a third of metastasized breast carcinoma patients have elevated ALP, usually up to 2 times. ALP elevations are most pronounced in cases of osteoblastic metastases and only mild in cases of osteolytic lesions such as multiple myeloma.

Liver involvement: the ALP activity in infiltration processes of the liver such as Hodgkin’s disease, leukemia, reticulum cell sarcoma or multiple liver metastases is dependent on the extent of involvement of the liver.

Tumor phosphatase: the phosphatase Regan isoenzyme occurs in approximately 3% of tumor patients, especially in those with lung carcinoma and ovarian and testicular carcinomas. However, barely half of the patients with Regan ALP have elevated total ALP. For further details, see Tab. 1.3-5 – ALP as biomarker in malignant tumors and bone metastases.

α-amylase

The prevalence of elevated α-amylase in pancreatic carcinoma is up to 40%. Elevated α-amylase often found in tumor patients does not relate to the pancreas but results, for example, from perforated ulcer, intestinal obstruction or reduced clearance in renal insufficiency.

Aminotransferases

Aminotransferases are non-specific biomarkers of malignant tumors. The prevalence of primary hepatocellular carcinoma in patients over 65 years of age with hepatitis C-RNA is higher than in those with normal aminotransferases /30/.

γ-glutamyl transferase (GGT)

Elevated GGT is measured in patients with liver metastases with average levels below 6 times the upper reference limit. Elevated GGT is rare in hepatocellular carcinoma and more common in cases of cholangiocarcinoma.

The ubiquitous enzyme LD can be elevated as a function of the tumor size and the extent of metastasis. It is a good biomarker in the monitoring and therapy assessment of malignant lymphomas. For further details, see Tab. 1.11-3 – Reference intervals of LD.

Table 1.1-12 Factors influencing serum enzyme activity /31/

Factor

ALP

Amylase

CHE

CK

GLD

AST

ALT

GGT

LAP

LD

Lipase

ACP

Alcohol

(+)

(+)

+

+

+

+

++

(+)

Diet

(+)

+

(+)

(+)

(+)

+

(+)

(+)

(+)

Lipid extraction from sample

+

(+)

+

+

++

++

Hemolysis

(+)

(+)

+

++

+

Drugs

+

+

+

+

+

+

+

+

+

+

+

+

Metabolites

+

+

+

+

Muscle activity

(+)

++

(++)

+

+

Physiological variations

+

+

+

+

Pregnancy, delivery

+

(+)

+

(+)

+

(+)

Table 1.1-13 Drug actions influencing serum enzyme activity /394041/

Enzyme

Drug action

ALP

Elevating: allopurinol, amsacrine, cotrimoxazole, cyclophosphamide, disopyramide, erythromycin, gold salts, isoniazid, ketoconazole, mercaptopurine, methotrexate, methoxyflurane, α-methyldopa, methyltestosterone, oxacillin, oxyphenisatine, papaverine, penicillamine, perhexiline, phenobarbital, phenylbutazone, phenytoin, primidone, propylthiouracil, ranitidine, trimethoprim/sulfamethoxazole, sulfasalazine, valproic acid

Reducing: clofibrate, oral contraceptives

ALT, AST

Elevating: acetaminophen, amiodarone, carbamazepine, disopyramide, heparin, oxacillin, oxyphenacetin, papaverine, paracetamol, penicillamine, perhexiline, phenylbutazone, phenytoin, ranitidine, rifampicin, salicylic acid, statins, streptokinase, trimethoprim/sulfamethoxazole, valproic acid

CK

Elevating: amoxapine, carbenoxolone, clofibrate, digoxin, halofenate, lidocaine, phenothiazine, succhinylcholine, statins, suxamethonium, theophylline

GGT

Elevating: carbamazepine, erythromycin, heparin, oral contraceptives (other than the micropill), oxacillin, phenytoin

Reducing: clofibrate

LD

Elevating: acetaminophen, anabolic steroids, aspirin/salicylates, chlorpromazine, erythromycin, gold salts, heparin, ketoconazole, naproxen, paracetamol, penicillamine, phenytoin, propylthiouracil, ranitidine, valproic acid

Table 1.2-1 Hepatic fibrosis staging based on scores and serum markers

Clinical and laboratory findings

AST-to-platelet ratio index (APRI) /10/

The APRI serves as a screening index for advanced hepatic fibrosis and cirrhosis (Ishak score ≥ 3) by combining the AST level and the thrombocyte count. The ratio of measured AST (U/L) vs. the upper reference value of AST divided by thrombocytes (109/L) x 100 is calculated.

APRI = AST ratio × 100/thrombocyte count (109/L)

Fibrosis: confirmed: APRI above 1.50; exclusion: APRI ≤ 0,50. Overall, 88% of patients had fibrosis at APRI above 1.50 and 85% did not at APRI ≤ 0.50.

Cirrhosis: confirmed: APRI above 2.00; exclusion: APRI ≤ 1,00. Overall, 57% of patients had cirrhosis at APRI above 2.00 and 93% did not at APRI ≤ 1.00.

BARD score /11/

This score is used to determine advanced fibrosis in non-alcoholic fatty liver disease (NAFLD). The following three variables are added: Body mass index (BMI) ≥ 28 kg/m2 = 1 point, AST/ALT ratio ≥ 0.80 = 2 points, diabetes mellitus = 1 point.

A score of 2–4 is associated with advanced fibrosis at an odds ratio of 17 (confidence interval: 9.2–31.9). The positive and negative predictive values for the diagnose of stage 3–4 fibrosis were 43% and 96%, respectively.

NAFLD fibrosis score /12/

This score is used to determine advanced fibrosis in NAFLD. It is obtained by adding the following six variables: Age (years); BMI (kg/m2); presence of diabetes mellitus or impaired fasting glucose (IFG), yes = 1, no = 0; AST/ALT ratio, thrombocyte count (nL) and serum albumin (g/dL). The following formula is used to calculate the fibrosis score:

Score = –1.675 + 0.037 × age + 0.094 × BMI + 1.13 × diabetes/IFG + 0.99 × AST/ALT – 0.013 × thrombocyte count – 0.66 × albumin

A value smaller than –1.455 is not associated with advanced fibrosis (classification according to Ref. /10/) (negative predictive value: 93%), a value > 0.676 is associated with the presence of advanced fibrosis (positive predictive value: 90%).

Enhanced Liver Fibrosis (ELF) score /13/

The ELF score is a fibrosis-specific algorithm composed of three parameters of the hepatic matrix metabolism: Tissue inhibitor of metalloproteinases-1 (TIMP-1), hyaluronic acid (HA) and N-terminal pro collagen III pro peptide (PIIINP), three proteins that are measurable in the serum /14/. The blood should always be collected in the morning under fasting conditions. All three proteins are measurable in immunoassays using a commercially available immunoassay analyzer. The ELF score is immediately calculated by the analyzer according to the equation:

ELF score = 2.494 + 0.846 LN(CHA) + 0.735 LN(CPIIINP) + 0.391 LN(CTIMP-1)

The cut-off value ≥ 7.7 indicates fibrotic tissue transformation with a diagnostic sensitivity of 93% at 33% specificity. The cut-off value ≥ 9.8 indicates mild to medium fibrotic transformation with a sensitivity of 41% at 98% specificity. Diagnostic sensitivity is 97% if transformation is already cirrhotic. It is also possible to distinguish between fibrotic and cirrhotic stages of the liver disease. The cut-off value ≥ 11.3 allows a distinction between cirrhoses and fibrotic stages at 97% diagnostic specificity in 83% of the cases. Valid diagnosis verification can only be expected with values of < 7.7 and > 11.3. As a rule, such values are no indication for liver biopsy because there is presumably no disease with a value of < 7.7 and cirrhosis is most likely present with a value of > 11.3. ELF score values between 9.8 and 11.3 cannot be unambiguously assigned to a specific fibrosis stage. Cirrhosis is definitely unlikely, but values in this range can be caused by active inflammation of the liver. Biological influence factors, especially age, gender and inflammation of the liver, can make clinical interpretation of the ELF score difficult. The ELF score increases with age; women have lower values than men. Values < 7.7 are predominantly found in young women; such values are rare in individuals > 60 years of age.

Forns score /15/

The Forns score was evaluated as predictor of fibrosis in patients with hepatitis C and is the result of logic regression analysis that combines the following parameters: age (years), GGT (U/L), cholesterol (mg/dL) and thrombocyte count (nL). The score is calculated according to the following equation:

Score = 7.811 – [3.131 LN thrombocyte count] + [0.781 LN GGT] + [3.467 LN age] – [0.014 cholesterol]. LN, natural logarithm.

If the score is below 4.2, significant fibrosis (Scheuer classification 2, 3, 4) can be excluded with a negative predictive value of 96%.

Guci index /16/

The Göteborg University Cirrhosis Index (GUCI) is used for the differentiation of hepatitis C patients with and without liver cirrhosis. The AST (U/L), INR and thrombocyte count (nL) are determined. The ratio of AST versus its upper reference limit is calculated.

Gucci index = AST ratio × INR × 100/thrombocyte count.

The cutoff value ≥ 1.0 indicates the presence of liver cirrhosis (Ishak fibrosis 5) at a sensitivity of 80% and 78% specificity. The positive predictive value is 31%, the negative predictive value is 97%.

Table 1.2-2 Criteria for orthotopic liver transplantation in acute liver failure

Criteria

Indications

King’s College criteria /17/

aPTT > 100 sec. (< 7% or INR > 6,7) or at least 3 of the following:

  • Adverse etiology (cryptogenic hepatitis, halothane hepatitis, drug-induced toxic injury).
  • Icterus more than 7 days before encephalopathy.
  • Age: < 10 yrs. or > 40 yrs.
  • aPTT > 50 sec. (> 15% and/or INR > 6.7)
  • Bilirubin > 17.5 mg/dL (300 μmol/L)

Criteria for paracetamol intoxication

Arterial pH < 7.3 or all 3 of the following:

  • aPTT > 100 sec.(< 7% or INR > 6.7)
  • Creatinine > 4 mg/dL (300 μmol/L)
  • Encephalopathy grade 3 or 4

Clichy criteria for potential recipients with viral hepatitis /18/

Encephalopathy grade 3 or 4 and:

  • Factor V < 20% for age < 30 yrs.
  • Factor V < 30% for age > 30 yrs.

Table 1.2-3 Mortality rate (%) after 3 months as a function of the MELD score /719/

Score

Liver cirrhosis(1

Transplant failure(2

< 10

4% (148)

5% (392)

10–19

27% (103)

6% (527)

20–29

76% (21)

10% (164)

30–39

83% (6)

10% (63)

> 40

100% (4)

26% (39)

1) This refers to the mortality rate of hospitalized cirrhotic patients. 2) Mortality rate in patients with different etiologies of liver failure. () Number of patients.

Table 1.2-4 Modified Child-Turcotte-Pugh score for severity assessment of a liver disease /8/

Variable

Score 1

Score 2

Score 3

Bilirubin (mg/dL)

< 2.0

2.0–3.0

> 3.0

Albumin (g/dL)

> 3.5

2.8–3.5

< 2.8

PTT (INR)

< 1.7

1.7–2.3

> 2.3

Ascites

None

Mild

Severe

Encephalopathy

None

Minimal

Advanced

The totals of scores of all 5 criteria are added. The following definition applies: class A: total score 5–6; Class B: total score 7–9; Class C: total score 10–15.

Table 1.2-5 Biomarkers in hepatopathies (see also Tab. 1.6-4 – Aminotransferases in patients with hepatopathies)

Clinical and laboratory findings

Viral infections

Viral infections of the hepatocytes are caused by hepatotropic viruses A to E and non-hepatotropic viruses. They are transmitted orally or parenterally. Viral hepatitides have much in common in regards to clinical, epidemiological, pathological and immunological aspects, but their etiology cannot be elucidated based on clinical symptoms and findings and the determination of liver enzymes. The further procedure required after the diagnosis of hepatocellular damage through the determination of aminotransferases is to determine viral and immunological biomarkers. It is important in this process to directly determine the viral genome.

Hepatitis A

Hepatitis A is usually transmitted by contaminated food; the incubation period is 3–6 weeks. It is not a chronic infection; the mortality rate in acute infection is approximately 0.2%.

Laboratory findings: virus detection in stool in the last third of the incubation period. Anti-HAV-IgM and anti-HAV-IgG are detectable while symptoms are acute; anti-HAV-IgM persists for 3–6 months. The sole detection of anti-HAV-IgG is evidence of previously suffered hepatitis or protection by vaccination.

Hepatitis B (HBV) /20/

It is assumed that 300–400 million individuals are infected with HBV worldwide. The chronification rate in infections in adulthood is below 5%. In cases of perinatal infection, 90% of the infected individuals pass into an asymptomatic HBV carrier state. About 500,000 individuals die of liver cirrhosis and hepatocellular carcinoma caused by chronic HBV infection worldwide every year, and 40,000 die of acute HBV infection. Information on the HBV status and infection markers are shown in Tab. 1.2-6 – Hepatitis B status.

– Acute HBV infection

Acute HBV infection progresses asymptomatically in newborns and infants and symptomatically in adults. The typical incubation period until the onset of symptoms is 3 months, but may last up to 6 months. HBsAg can be detected in serum 4–10 weeks after infection. Most infections in adults are self-limiting and the patients recover completely if HBsAg is eliminated from the blood and anti-HBs can be detected. Patients who are coinfected with the hepatitis C or hepatitis D virus have an increased risk of severe HBV hepatitis. HBV occurs in 8 genotypes A to H.

Laboratory findings: ALT, HBsAg, anti-HBc (total and IgM), HBeAg and anti-HBe. HBsAg is negative and anti-HBc is positive in approximately 5% of acute HBV infections. In this case, the anti-HBc-IgM or HBV DNA must be determined. In cured HBV infections, HBsAg is negative, anti-HBc is positive and anti-HBs is positive. In the quantitative analysis of HBV DNA, 1 IU roughly corresponds to 5 virus copies/mL.

– Chronic HBV infection /21/

Chronic HBV infection affects more than 350 million people worldwide. Globally more than 50 million new cases of HBV infection occur annually  /22/. The vast majority of those affected are from the Asia-Pacific region and are mostly infected perinatally or during early childhood. The progression of chronic hepatitis B is a multifactorial, multistage progress involving interactions among host, environmental, and viral factors. Chronic inflammation associated with human immune responses to HBV infection increases damage and proliferation of hepatocytes  /23/.

Assessment of patients with chronic HBV infection Tab. 1.2-7 – Assessment of patients with chronic HBV infection.

HBV marker: HbsAg, HBeAg/anti-HBe, HBV DNA.

Liver disease marker: ALT, non-invasive marker of fibrosis (elastography or biomarkers), liver fibrosis in selected cases.

Classification of chronic HBV infection into 5 phases /24/

The phases of the chronic HBV infection are not necessarily sequential.

  • Phase 1: HBeAg positive chronic HBV infection, previously termed immune tolerant phase; characterized by the presence of serum HBeAg, very high concentrations of HBV DNA, and ALT persistently within the normal range. In the liver there is minimal or no liver necroinflammation or fibrosis but a high level of HBV DNA integration and clonal hepatocyte expansion suggesting that hepatocarcinogenesis could be already under way in this early phase of infection. The immune tolerant phase is more frequent and more prolonged in individuals infected perinatally and is associated with preserved HBV specific T-cell function at least until young adulthood. During this phase, the rate of spontaneous HBeAg loss is very low. Because of high levels of viremia, these patients are highly contagious.
  • Phase 2: The immune reactive HBeAg positive phase is characterized by HBeAg positivity, high levels of HBV DNA and elevated ALT. In the liver there is a moderate or severe necroinflammation and accelerated progression of fibrosis It may occur after several years of the first phase and is more frequently and /or more rapidly reached in individuals infected during adulthood. The outcome of this phase is variable. Most patients can achieve seroconversion and HBV DNA suppression and enter the HBeAg negative infection phase. Other patients may fail to control HBV and progress to the HBeAg-negative CHB phase for many years.
  • Phase 3: HBeAg negative chronic HBV infection, previously termed inactive HBV carrier phase, is characterized by the presence of anti-HBe, undetectable or low (below 2.000 IU/mL) HBV DNA levels and normal ALT. Some patients in this phase, however, may have HBV DNA levels >2.000 IU/mL (usually below 20.000 IU/mL) accompanied by persistently low ALT and only minimal hepatic necroinflammatory activity and low fibrosis. These patients have low risk of progression to cirrhosis or hepatocellular carcinoma if they remain in this phase, but progression to chronic hepatitis B, usually in HBeAg-negative patients, may occur spontaneously in 1-3% of cases per year. Typically, such patients may have low levels of serum HBsAg (<1.000 IU/mL).
  • Phase 4: HBeAg negative chronic hepatitis B is characterized by the lack of serum HBeAg usually detectable with anti-HBe, and persistent and fluctuating moderate to high levels of serum HBV DNA (often lower than in HBeAg positive patients), as well as fluctuating or persistently elevated ALT values. The liver histology shows necroinflammation and fibrosis. Most of these individuals harbour HBV variants in the pre core and/or the basal core promoter regions that impair or abolish HBeAg expression. This phase is associated with low rates of spontaneous disease remission.
  • Phase 5: HBsAg-negative phase is characterized by serum negative HBsAg and positive antibodies to HBcAg (anti-HBc), with or without detectable antibodies to HBsAg (anti-HBs). This phase is also known as occult HBV infection. In rare cases, the absence of HBsAg could be related to the sensitivity of the assay used for detection. Patients in this phase have normal ALT and usually, but not always, undetectable serum HBV DNA. HBV DNA can be detected frequently in the liver. HBsAg loss before the onset of cirrhosis is associated with a minimal risk of cirrhosis, decompensation and hepatocellular carcinoma (HCC). However, if cirrhosis has developed before HBsAg loss, patients remain at risk of HCC therefore HCC surveillance should continue. Immunosuppression may lead to HBV reactivation in these patients.

Treatment of chronic hepatitis B

The indications for treatment are generally the same for both HBeAg positive and HBeAg-negative CHB. This is based on the combination of three criteria  /24/:

  • Serum HBV DNA concentrations
  • Serum ALT levels
  • Severity of liver disease

Recommendations for treatment /24/:

  • All patients with HBeAg-positive or negative CHB, defined by HBV DNA >2.000 IU/mL, ALT above the upper reference interval value and/or at least moderate liver necroinflammation or fibrosis.
  • Patients with compensated or decompensated cirrhosis with any detectable HBV DNA concentration and regardless of ALT level.
  • Patients with HBV DNA >20.000 IU/mL and ALT higher than 2-fold the upper reference interval value, regardless of the degree of fibrosis.
  • Patients with HBeAg-positive HBV infection, defined by persistently normal ALT and High HBV DNA concentrations if they are older than 30 years regardless of the severity of liver histological lesions.
  • Patients with HBeAg-positive or negative HBV infection and family history of hepatocellular carcinoma or cirrhosis and extrahepatic manifestations even if typical treatment indications are not fulfilled.

Treatment options

There are two main treatment options for CHB patients: treatment with nucleoside analogues (NA; lamivudine, adefovir dipivoxil, entecavir, telbivudine tenovofir disoproxil fumarate, tenofovir alafenamide) or pegylated interferon alpha (PegIFNα).

NA therapy virological responses  /24/

  • Virological response is defined as undetectable HBV DNA by a sensitive PCR assay with a limit of detection of 10 IU/mL.
  • In patients who discontinue NA, sustained off-therapy virological response could be defined as serum HBV DNA levels <2,000 IU/mL for at least 12 months after therapy.
  • Primary non-response is defined by less than one log10 decrease of HBV DNA after 3 months of therapy.
  • Partial virological response is defined as a decrease in HBV DNA of more than 1 log10 IU/mL decrease after at least 12 months therapy in compliant patients.
  • Virological breakthrough is defined as a confirmed increase in HBV concentration of more than 1 log10 IU/mL compared to the nadir (lowest value) HBV DNA concentration on-therapy; it may precede a biochemical breakthrough, characterized by an increase in ALT levels.

Peg IFNα therapy virological responses  /24/

  • Virological response is defined as serum HBV DNA levels <2,000 IU/mL. It is usually evaluated at 6 months and at the end of therapy.
  • Sustained off-therapy virological response is defined as serum HBV DNA levels <2,000 IU/mL for at least 12 months after the end of therapy.
  • Serological responses for HBeAg are HBeAg loss and HBeAg seroconversion, e.g., HBeAg loss and development of anti-HBe.
  • Serological responses for HBsAg are HBsAg loss and HBsAg seroconversion, e.g., HBsAg loss and development of anti-HBs.
  • Biochemical response is defined as a normalization of ALT levels. Since ALT often fluctuates over time, a minimum follow-up of at least 1 year post-treatment with ALT determinations is required to confirm off treatment biochemical response.

– Liver cirrhosis, hepatocellular carcinoma (HCC)

Chronic HBV infection is a risk factor of liver cirrhosis and hepatocellular carcinoma (HCC). The increase in incidence is 5% every 10 years in patients who acquired an HBV infection perinatally. The risk of liver cirrhosis and HCC is low in individuals in the immune tolerance phase and in the inactive carrier phase.

Laboratory findings: patients, who remain in the immune clearance phase for longer periods and show a viral load < 104/mL copies, have a HCC risk of 2.1% at a viral load of 107 copies/mL, and of 19.8% after 13 years. The ALT is also associated with the HCC risk. The risk starts to increase if values are at the high end of the normal range (30–45 U/L); upper reference limit: 45 U/L /25/.

Hepatitis C virus (HCV) /26/

HCV infection is a worldwide problem and the main cause of chronic liver disease. Approximately 180 million individuals are infected worldwide; about 80% of these are viremic. HCV infection is the most important cause of death in liver diseases and in the USA the most common indication for orthotopic liver transplantation. Six genotypes of HCV (genotypes 1–6) are distinguished. Genotype 1 is further divided into subtypes 1a and 1b. Types 1, 2 and 3 are most common in the USA and in Germany. In Germany, the proportion of subtype 1a is 28% and that of subtype 1b is 50% in all HCV infections. HCV is transmitted parenterally; essential causes include infections in drug addicts, infusion of blood and blood components before the year 1992, sexual transmission from an infected partner, needle stick injuries, piercing, transplacental transmission. The incubation period is 2–6 months.

Clinical aspects: the differentiation between acute and chronic infections depends on the clinical presentation, especially if jaundice or elevated ALT are present or were historically present. During the prodromal phase, the symptoms of acute hepatitis C are similar to those of hepatitis B, albeit not as pronounced. The course of the disease is usually asymptomatic or characterized by non-specific clinical symptoms. 30–70% of the patients have an anicteric course. 55–80% of the individuals who develop acute hepatitis will remain HCV infected. Spontaneous recovery is more common in infected children and young women than in older individuals suffering from acute hepatitis.

Laboratory findings: essential methods for the detection of an infection include immunoassays for the serological diagnosis of specific antibodies against HCV (anti-HCV) and the determination of HCV RNA. Diagnostic specificity of the immunoassays is higher than 99%. Wrong positive results are obtained if HCV prevalence is very low in a population. Wrong negative results can be obtained in immunosuppressed (HIV infected) patients, cases with hypogammaglobulinemia or agammaglobulinemia, organ-transplant patients and hemodialysis patients. The molecular biological assays for the detection of HCV RNA have a lower detection limit of 10–50 IU/mL. The conversion factor in copies/mL is dependent on the relevant method used. Anti-HCV can be detected at the earliest by 8–12 weeks and HCV RNA by 2 weeks following an infection. The findings from ALT, anti-HCV and HCV RNA lead to the following result patterns and assessments:

  • Anti-HCV and HCV RNA positive, ALT elevated or recently elevated; acute HCV infection or acute hepatitis of different etiology in cases of chronic HCV infection.
  • Anti-HCV positive, HCV RNA negative; acute HCV infection with transient clearance of HCV RNA or wrong positive or negative laboratory determination or the period of reconvalescence of an acute HCV infection. The determination of anti-HCV and HCV RNA should be repeated after 4–6 months for verification.
  • Anti-HCV negative, HCV RNA positive; early stage of acute infection at which antibodies have not yet developed, or presence of a chronic infection in an immunosuppressed patient, or incorrect laboratory determination of HCV RNA. The determination of anti-HCV and HCV RNA should be repeated after 4–6 months for verification.

– Chronic hepatitis C virus infection

About 70% to 80% of patients infected with HCV develop chronic hepatitis C. Chronic progression is characterised by progressive liver damage, which can lead to cirrhosis of the liver after 20 to 25 years in 2% to 35% of those affected. The progression toward liver cirrhosis is faster in older individuals, obese individuals, immunosuppressed patients and alcoholics. If the infection occurs in childhood or young women, the risk is only 1–3% over a period of 20–30 years. The cumulative 5-year risk of developing hepatocellular carcinoma for patients with cirrhosis of the liver is 17%.

European Association for the Study of the Liver (EASL) recommendations on treatment of hepatitis C /27/

Screening for chronic hepatitis C: screening is based on the detection of anti-HCV antibodies. If anti-HCV antibodies are detected, HCV RNA or alternatively HCV core antigen if HCV RNA assays are not available should be determined to identify patients with on-going infection. HCV RNA detection and quantification should be made by a sensitive assay with a lower limit of detection of 15 IU/mL. Of the HCV genotypes 1 to 6 found worldwide, most infections found in Germany are caused by HCV genotype 1 (70% to 80%) and genotypes 2 and 3. Genotype 4 is found mainly in the Middle East, genotype 5 in South Africa, and genotype 6 in South-east Asia.

Pre therapeutic assessment

  • The causative relationship between HCV infection and liver disease should be established.
  • Liver disease severity should be assessed prior to therapy.
  • HCV RNA detection and quantification should be made by a sensitive assay with a lower limit of detection of 15 IU/mL.
  • The HCV genotype and genotype 1 subtype (1a or 1b) must be assessed prior to treatment initiation and will determine the choice of therapy, among other parameters.

Goals and endpoints of HCV therapy

  • The goal of therapy is to cure HCV infection to prevent hepatic cirrhosis, decompensation of cirrhosis, hepatocellular carcinoma (HCC), severe extrahepatic manifestations and death.
  • The endpoint of therapy is undetectable HCV RNA in blood by a sensitive assay (lower limit of detection 15 IU/mL) 12 weeks and/or 24 weeks after the end of treatment.
  • Undetectable HCV core antigen 12 weeks and/or 24 weeks after the end of treatment is an alternative endpoint of therapy in patients with detectable HCV core antigen prior to therapy if HCV RNA assays are not available or not affordable.
  • In patients with advanced fibrosis and cirrhosis, HCV eradication reduces the rate of decompensation and will reduce, albeit not abolish, the risk of HCC. In these patients the surveillance of HCC should be continued.

Peg interferon and ribavirin treatment of chronic hepatitis C

The patients are treated with peg interferon and ribavirin. Patients infected with HCV genotype 1 are usually harder to treat for reasons that are not yet fully clear. Early virologic response (EVR; no evidence of HCV RNA at week 12 of treatment), rapid virologic response (RVR; no evidence of HCV RNA at week 4 of treatment during dual therapy) and sustained virologic response (SVR; no evidence of HCV RNA 24 weeks after treatment, a surrogate marker for successful HCV treatment) are criteria for treatment success. The SVR is the most important criterion for effective treatment. It is generally regarded as virological cure although HCC can still occur years later, especially in patients with liver cirrhosis. Determination of the viral load before treatment start and the viral genotype are two important prerequisites for achieving a high SVR rate. More patients reach the SVR state if their viral load is below 600,000 IU/mL and they do not have genotype 1. Side effects of peg interferon and ribavirin therapy include influenza-like symptoms, depression, neutropenia below 1.5 × 109/L in 18–20% of the cases and anemia with a nadir in treatment week 6–8 in one third of the patients.

Measuring the HCV RNA clearance rate: helpful for predicting probable response and optimal duration of treatment. In order to determine the clearance, it is necessary to measure the viral kinetics along with their assessment criteria EVR and RVR.

Assessment criterion EVR: the inability to achieve a reduction of the HCV RNA load by 2 log10 IU/mL by week 12 of therapy indicates non-response in patients with genotype 1; 97–100% of these patients do not reach SVR. No evidence of HCV RNA after 12 weeks (EVR) indicates SVR with a predictive value of 83%. In contrast, the predictive value for 2 log10 reduction is only 21%.

Assessment criterion RVR: the early response before 12 weeks of treatment implies a high predictive value for SVR independently of the genotype or the treatment regime. About 66% of the patients with a genotype 2 or 3 infection reach the RVR, compared to only 15–20% of the patients with a genotype 1 infection.

In Germany, the response rates to peg interferon and ribavirin combination treatment (dual therapy) are 40–50% in cases of genotype 1 and 70–80% in genotypes 2 and 3 /28/. The combination treatment is individualized depending on the genotype and extent of viral load at the start of treatment and its decrease during the first weeks of treatment. The combination of peg interferon and ribavirin with the protease inhibitors boceprevir or telaprevir (triple therapy) shows sustained response rates of 67–75% in the treatment of HCV genotype 1 infections. Patients who previously did not respond to dual therapy also benefit from triple therapy.

Hepatitis D (HDV) /29/

The HD virus contains a single-stranded RNA genome of 1.7 kb. This RNA viroid depends on the helper function provided by the HBV envelope proteins for viral replication and pathogenicity. Its transmission is similar to that of the HBV – mainly parenterally via the blood, physical contact, injection with contaminated needles used by drug addicts, sexual contacts and perinatally.

The following distinctions are made in HDV transmission:

  • HDV co-infection (i.e., simultaneous transmission of HDV and HBV). The biomarker course and clinical course are similar to those in HBV infection, which is characterized by the occurrence of HBsAg in serum and HBcAg in the hepatocytes 6–12 weeks after infection. In addition, HDAg occurs 3–4 weeks later in cases of co-infection. Antibodies against HDAg are detectable shortly afterwards. Co-infection is self-limiting and heals completely in 90% of the cases. In some cases, co-infection and the combination of associated effects may cause severe to fulminant hepatitis.
  • HDV superinfection (i.e., infection of chronic HBsAg carriers with HDV). Superinfection is suggested clinically if chronic HBsAg carriers suffer from severe to fulminant hepatitis. Patients who survived the course of this disease experience fast progressing chronic hepatitis, liver cirrhosis and death from liver failure in many cases.

Laboratory findings: if an HDV infection is suspected, the determination of anti-HDV (IgG+IgM) is generally performed and, if positive, the HDV RNA is determined.

HDV co-infection: in HDV co-infection, anti-HDV-IgM and circulating HDV RNA are transiently detectable 2–4 weeks after HBsAg positivity, but cannot be detected anymore several weeks later. Co-infection is suggested in cases of severe hepatitis if the following constellation exists: HBsAg positive, anti-HBc positive, anti-HBc-IgM negative because a high titer of anti-HBc-IgM would be expected in a fulminant course. A two-phase pattern of the aminotransferases is also observed in many cases; the second increase (3–4 weeks later) is HDV-related.

HDV superinfection: HBV DNA concentrations and the titer of HBsAg decrease temporarily 2–6 weeks after the superinfection; HDV RNA can be detected a week after the infection. Anti-HDV-IgG and anti-HDV-IgM become positive, followed by persistently positive anti-HDV-IgG and detectable HDV RNA. Anti-HDV-IgM can persist for years. HDV superinfection causes a pronounced increase in aminotransferases.

Hepatitis E /30/

The HE virus (HEV) is a small, non-enveloped virus with a single-strand genome of 7.2 kb. Four genotypes are distinguished: genotype 1 (Burmese isolate), genotype 2 (Mexican isolate), genotype 3 (U.S. isolate), genotype 4 (Chinese isolate). The course of the infection is comparable with that of hepatitis A and is usually self-limiting. As a rule, the virus is transmitted fecally/orally. Hepatitis E is a zoonotic disease; most infections in developed countries are of type 3 and transmitted by domestic pigs and wild boar. Inadequately cooked pig innards or wild boar meat are probable sources of infection. HEV has also been detected in other species such as birds, dogs and rats besides pigs. The incubation period is 2–8 weeks.

Clinical aspects: the disease typically starts with fever, fatigue and jaundice. Many infections are only associated with mild symptoms and therefore are not diagnosed. The virus is excreted in feces during the incubation period until the later stage of the disease. While mortality is 0.5-4% in children and men, it can reach up to 20% in pregnant women in the last trimester of pregnancy due to the development of fulminant hepatitis. Disseminated intravascular coagulation and encephalopathy can also occur. HEV infections in patients with alcohol-toxic hepatitis or chronic liver disease can lead to fulminant hepatitis. Chronic HEV infections have also been described in organ transplantation.

Laboratory findings: if an HEV infection is suspected, it is recommended to determine the anti-HEV-IgM and anti-HEV-IgG in serum. HEV infection is only likely if antibodies are detected and clinical symptoms are present. In HEV infection, anti-HEV-IgM and anti-HEV-IgG can be detected 1–4 weeks after the onset of clinical symptoms in approximately 90% of the cases. Anti-HEV-IgM persists for about 3 months, while anti-HEV-IgG persists for a very long time. The prevalence of anti-HEV-IgG in some parts of Europe is 20%. This indicates that many infections occur with mild symptoms. The first sampling should be followed by another one about 8–10 days later to provide evidence of an increase in antibodies. A reliable diagnosis of hepatitis E is based on the detection of HEV RNA in feces or blood during acute infection, but can also be performed a week before the onset of clinical symptoms. Aminotransferases reach peak levels when HEV antibodies occur (i.e., 1–4 weeks after the onset of clinical symptoms).

Hepatitis (other pathogens) /31/

Diseases caused by non-hepatotropic viruses and bacteria with flu-like symptoms can be associated with concomitant hepatitis and increased aminotransferases. If there is no evidence of hepatotropic viruses in the serological findings, the following should be determined: adenoviruses, herpes group viruses (e.g. Epstein-Barr virus, Cytomegalo virus) and, in babies, Herpes simplex viruses and enteroviruses (Coxsackie viruses of groups A and B, ECHO viruses). Elevated aminotransferases are also occasionally measured in cases of measles and rubella infections. Bacterial pneumonias can also be associated with liver involvement. Diarrheal diseases caused by Salmonella and Rotavirus, as well as rare infections (listeriosis, leptospirosis, toxoplasmosis) can also result in a hepatitic picture with moderately elevated aminotransferases that normalize during remission of the disease.

Autoimmune liver diseases

Autoimmune liver diseases are classified into the syndromes autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis. AIH should be considered in cases with a persistent or relapsing course and a hepatitis enzyme pattern.

– Autoimmune hepatitis (AIH) /3233/

90% of AIH patients are women. Diagnostic criteria include the following conditions: evidence of associated antibodies, elevated serum-IgG, corresponding liver histology, absence of viral hepatitis. AIH is serologically heterogeneous and classified into three subgroups, where AIH type 1 is most common /34/:

  • AIH type 1 with antinuclear antibodies (ANA) and anti smooth muscle antibodies (anti-SMA)
  • AIH type 2 with antibodies against liver-kidney microsomes (anti-LKM-1)
  • AIH type 3 with antibodies against soluble liver antigen/liver-pancreas antigen (anti-SLA/LP).

– Primary biliary cirrhosis (PBC) /35/

PBC is a chronic granulomatous cholangitis associated with the presence of anti-mitochondrial antibodies (AMA). Environmental factors are thought to play a role, and genetic factors are also supposedly involved. Association with variants of the HLA class II, especially IL-12A and IL-12RB2, suggests that the interleukin-12 immunoregulatory signaling axis is relevant to the pathophysiology of PBC /36/. The disease mainly affects women at 40–60 years of age and can be associated with Hashimoto’s thyroiditis and the sicca syndrome. Progressive destruction of the small bile ducts and the development of liver cirrhosis occur during the course of the disease.

Laboratory findings: most patients show mild elevation of aminotransferases, elevated ALP and elevated IgM. AMA are elevated in 95% of the patients, and ANA and anti-SMA are elevated in about 50%. AMA-negative patients show all characteristics of AMA-positive PBC patients, including the presence of ANA and anti-SMA. The following applies to patients without liver cirrhosis:

  • The extent of ALP elevation is associated with the extent of ductopenia and inflammation
  • The aminotransferase level and the IgG concentration are correlated with periportal and lobular necrosis and inflammation
  • The concentration of bilirubin is an indicator of ductopenia and piecemeal necrosis.

Increasing bilirubin and immunoglobulin concentrations and a decrease in albumin and thrombocyte count indicate the development of liver cirrhosis and portal hypertension.

– Primary sclerosing cholangitis (PSC) /37/

PSC is a chronic cholestatic liver disease characterized by inflammation and fibrosis of the intrahepatic and extrahepatic bile ducts and resulting in multifocal bile duct strictures.

It is an immune-mediated progressive disease that can develop into liver cirrhosis with portal hypertension and liver failure in many patients.

PSC is associated with chronic inflammatory bowel disease in approximately 70% of the cases and affects men at 25–45 years of age in two thirds of the cases. The incidence is 1–6 in 100,000 per year. PSC manifests clinically by upper abdominal pain, pruritus, anorexia and fever. PSC of the small bile ducts takes a benign course and does not shorten the life expectancy of those diagnosed with it. By contrast, PSC of the large bile ducts has a high carcinogenic potential. For example, the risk of cholangiocellular carcinoma is 141-fold, that of pancreatic carcinoma is 14-fold higher and that of colorectal cancer is 10-fold higher than normal. A carcinoma is the cause of death in 44% of these patients /38/.

Laboratory findings: elevated ALP is the most common clinical laboratory result, but PSC cannot be excluded if ALP is normal. Aminotransferases can be elevated 2–3-fold. The bilirubin is mostly normal and IgG is mildly elevated in 60% of the cases at the time of diagnosis.

– IgG4-associated cholangitis (IAC) /39/

IAC is characterized by multi focal inflammatory and fibrosing stenosis of the intrahepatic and extrahepatic bile ducts. Contrary to PSC, the strictures are typically infiltrated by IgG4-expressing plasma cells. The concentration of IgG4 in serum can be elevated.

Alcoholic liver diseases /40/

Chronic alcohol consumption can cause various types of liver injury. The spectrum of alcoholic liver diseases ranges from steatohepatitis (fatty liver) to alcoholic hepatitis to chronic hepatitis with fibrosis or cirrhosis. Alcohol has a liver toxic effect; women are twice as sensitive to alcohol toxicity as men.

The diagnosis of alcoholic liver diseases is based on a combination of characteristics, including: alcoholic history, clinical detection of a liver disease and biomarkers. Alcoholic liver disease is assumed to develop in women who have two drinks a day and in men who have more than three. A drink is equal to 9.8 g of alcohol in Europe, 12 g of alcohol in the U.S.A. and 23.5 g of alcohol in Japan on average.

– Steatohepatitis

Alcoholic fatty liver develops in about 90% of individuals who drink more than 60 g of alcohol a day. The hepatocytes contain macro vesicular droplets of triglycerides that disappear again with abstinence after 4–6 weeks. However, steatosis is a predisposition for fibrosis and cirrhosis in individuals who continue to drink (more than 40 g/day). Even with abstinence, progression is thought to occur in 5–15% of the cases. Uncomplicated fatty liver is clinically normal; a small proportion of patients complain of upper abdominal fullness due to enlargement of the liver.

– Liver fibrosis/cirrhosis

Perivenular fibrosis and fibronectin deposition occur in 40–60% of patients who drink more than 40–80 g of alcohol a day for 25 years on average. The risk of liver cirrhosis in these drinkers is 6–41%.

– Alcoholic hepatitis /41/

Alcoholic hepatitis is a clinical syndrome with jaundice and liver failure that occurs after decades of severe alcohol abuse (> 100 g/day). The typical age of patients is about 40 years.

Laboratory findings: alcoholic fatty liver can be associated with a mild elevation of GGT and ALT; the mean corpuscular volume of the erythrocytes and the carbohydrate deficient transferrin can be elevated. In alcoholic hepatitis, aminotransferases are elevated up to 300 U/L and bilirubin is higher than 5 mg/dL (86 µmol/L). The AST/ALT ratio is greater than 2.

NAFLD and NASH /4243,/

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent form of chronic liver disease and affects about 25% of the global adult population. NAFLD is defined as steatohepatitis in individuals who drink no or little alcohol. Fibrosis develops among patients with non-alcoholic steatohepatitis (NASH). Liver related morbidity and mortality related to NAFLD are substantial and fibrosis seems to be the strongest independent predictor of outcome. NAFLD is a metabolic disorder strongly associated with visceral obesity and insulin resistance. An allele in PNPLA3 (rs738409[G] encoding I148M) shows strong association with high hepatic fat content and hepatic inflammation. NASH is a liver disease that may progress to fibrosis, cirrhosis and hepatocellular carcinoma. NAFLD is the most common cause of chronic liver disease in children and adults. Incidence is growing due to the fact that an increasing number of individuals are overweight and develop diabetes type 2. NAFLD patients have clinically significant comorbidities such as increased body mass index, increased hip circumference and central obesity, glucose intolerance, diabetes type 2, hyperlipidemia, metabolic syndrome and hypothyreosis. The prevalence of NASH is about 3% in adolescents and up to 10–15% in adults. Middle-aged non-diabetics with a fatty liver index above 60 show association with increased carotid intima thickness, increased cardiovascular risk and reduced insulin sensitivity. Histologically, NASH differs from simple steatosis by its macrovesicular character (the lipid droplets vary from small to large where a hepatocyte is occupied by one large droplet), ballooning degeneration of the hepatocytes with or without Mallory bodies, lobular inflammation and zone 3 pericellular fibrosis.

Most patients are clinically normal or have a feeling of pressure in the upper abdomen due to soft hepatomegaly. Diagnosis is based on the exclusion of other liver diseases (chronic hepatitis B or C, alcoholic liver disease) and the search for comorbidities.

Laboratory findings: conventional biomarkers (ALT, GGT, AST/ALT ratio) and the mean corpuscular volume of the erythrocytes (MCV), which play a certain role in alcoholic liver diseases, contribute little to the diagnosis of NAFLD. Initially, the ALT is mildly elevated and higher than the AST; the ratio is reversed upon transition to NASH. However, the aminotransferase levels can only be used to a limited degree to predict hepatic histology. In contrast, the alcoholic liver disease/NAFLD index score is significant in NAFLD diagnosis. Important diagnostic assays for comorbidities include: fasting blood glucose, HbA1C, insulin, HOMA-IR or QUICKI, cholesterol, triglycerides, C-reactive protein, NAFLD fibrosis score (Tab. 1.2-1 – Hepatic fibrosis staging based on scores and serum markers) and BARD score (Tab. 1.2-1 – Hepatic fibrosis staging based on scores and serum markers). Promising assays include the cytokeratin-18 fragment and the Fibro test (Tab. 1.2-1 – Hepatic fibrosis staging based on scores and serum markers). The following autoantibody findings are considered to be epiphenomena that occur in up to one third of patients with NAFLD: ANA in titer below 1: 320, anti-SMA and AMA below 1: 40. Elevated AST, GGT and anti-SMA indicate increasing fibrotization in NASH.

Liver cirrhosis  /44/

Cirrhosis can arise in consequence of an infectious, exogenous toxic, toxic allergic autoimmune, or vascular process or an inborn error of metabolism. The commonest causes of cirrhosis in the Western industrialized countries are alcoholic or non-alcoholic fatty liver disease and viral hepatitis B or C. Cirrhosis is histologically characterized by fibrous septa between the portal fields; in comes in micro- and macro nodular forms. The typical findings in liver cirrhosis include cutaneous signs of liver disease, a firm liver on palpation and certain risk constellations, e.g. metabolic syndrome, heavy alcohol consumption, exposure to hepatotoxic substances, and the use of hepatotoxic medications. Cirrhosis is the end stage of chronic liver diseases that progress over years or decades.

Laboratory findings: Measuring concentrations of ALT (an indicator of hepatic inflammation) and GGT (an indicator of cholestasis and impaired hepatic metabolism) is indicated as a screening measure presenting at the primary care physician, even if asymptomatic. If the screening tests point to liver disease methods for estimating liver function (decrease of albumin and cholinesterase, increase of INR) and for the extent of the hepatic fibrosis (decrease of thrombocyte count, increase of the hyaluronic acid concentration, and increase of the AST-to-platelet ratio index, APRI) are recommended.

Hepatocellular carcinoma (HCC) /45/

As a rule, HCC develops on the basis of a pre-existent liver disease, especially liver cirrhosis. (see also Tab. 1.6-4 – Aminotransferases in patients with hepatopathies, here: Liver metastases). HCC belongs to the ten most frequent malignant tumors worldwide and is even the most frequent malignant tumor in Southeast Asian countries. It is a complication of liver cirrhosis in 80% of the cases and diagnosed in 2.5–7% of liver cirrhosis patients a year. The cause of liver cirrhosis plays an essential role. Patients with liver cirrhosis based on hepatitis B and C, hemochromatosis and tyrosinemia have an especially high risk of HCC, whereas the risk is low in cases of cirrhosis due to PBC, PSC and Wilson’s disease. HCC can also develop in hepatitis B patients without cirrhosis, but rarely does so in hepatitis C patients. A significant proportion of liver cirrhosis is due to NASH. Hence, a higher rate of HCC is also to be expected in these patients – mainly those with a body mass index higher than 35 kg/m2.

Clinical symptoms of HCC include reduced fitness, weight loss, fever, night sweats and pain due to stretching of the liver capsule. Para neoplastic syndromes include: Polyglobulia, dysfibrinogenemia, hypercholesterolemia, hypercalcemia, hypoglycemia, gynecomastia, testicular atrophy and porphyria cutanea tarda. Acute liver failure and gastrointestinal hemorrhage are the most common causes of death in HCC.

Laboratory findings: patients with Child-Pugh stages A and B (see Section 5.2) with cirrhosis due to hepatotropic viruses, alcohol abuse or hemochromatosis should have their concentration of α-fetoprotein (AFP) determined every 3 to 6 months as a precaution. Tumor detection with two imaging methods and AFP concentrations higher than 400 µg/L are clearly indicative of HCC. Elevated values confirm the diagnosis of HCC; fluctuating values can also result from liver regeneration during hepatitis. In cases with HCC smaller than 3 cm in diameter, AFP determination is inferior to imaging, but diagnostic sensitivity of des-gamma-carboxyprothrombin (DCP) and lens culinaris agglutinin-reactive fraction of AFP (AFP-L3) is higher /46/. Laboratory blood tests should be performed prior to therapy (blood count, PT, APTT, bilirubin, aminotransferases, GGT, creatinine). Indication criteria for orthotopic liver transplantation are shown in Tab. 1.2-1 – Hepatic fibrosis staging based on scores and serum markers.

Drug effects

Up to 1% of drug-exposed patients show adverse drug events in the liver. However, less than 5% of acute hepatitis and an even smaller percentage of chronic hepatitis are caused by hepatotoxicity. Severe adverse drug events occur in old individuals, in particular, and drugs are responsible for 20–75% of cases of acute liver failure. A distinction is made between obligatory hepatotoxins where liver damage is predictable and facultative hepatotoxins where liver damage is not predictable. The first include, for example, paracetamol, methotrexate and isoniazid. The hepatotoxic effect often comes from the metabolic products of the drugs. For example, unpredictable hepatotoxicity is caused by metabolic and toxic-allergic mechanisms with neoantigen formation. A relationship between drug and hepatotoxicity is considered if liver injury occurs between 5 and 90 days after drug intake.

The following spectrum of liver diseases can be induced by the drugs listed as examples below /48/:

  • Fatty liver: aspirin, HAART, tetracycline, tamoxifen
  • Acute/fulminant hepatitis: halothane, INH, paracetamol, sulfonamides, troglitazone
  • Chronic hepatitis: diclofenac, minocycline, α-methyldopa, nitrofurantoin
  • Granulomatous hepatitis: allopurinol, carbamazepine, hydralazine
  • Cholestasis: androgens, oral contraceptives
  • Cholestatic hepatitis: chlorpromazine, clavulanic acid, macrolides
  • Chronic cholestasis: chlorpromazine, flucloxacillin
  • Steatohepatitis: amiodarone, tamoxifen
  • Veno-occlusive damage: cytostatics
  • Adenoma: oral contraceptives
  • Hepatocellular carcinoma: anabolic steroids.

Laboratory findings: elevated aminotransferase (see Section 1.6 – Alanine aminotransferase (ALT), Aspartate aminotransferase (AST)), ALP (see Section 1.3 – Alkaline phosphatase (ALP)) and GGT (see Tab. 1.6-4 – Aminotransferases in patients with hepatopathies) levels can be used to roughly distinguish between hepatitic and cholestatic courses of drug-induced liver injury.

Sarcoidosis

Sarcoidosis is a granulomatous disease involving many organs, including the liver. In acute sarcoidosis, the liver is rarely involved. In chronic sarcoidosis, however, he liver is affected in about 75% of the cases, but without functional restrictions. The granulomas are usually small and localized in the portal regions. Clinical manifestations with cholestasis and portal hypertension occur in rare cases. Intrahepatic sarcoidosis can simulate PBC or PSC.

Laboratory findings: angiotensin-converting enzyme (see Section 1.5.5.1 – Sarcoidosis), Kveim test, ALT, ALP.

Preeclampsia/eclampsia

Preeclampsia/eclampsia, the HELLP syndrome, acute fatty liver of pregnancy and intrahepatic cholestasis result in liver injury during pregnancy (see Tab. 1.6-4 – Aminotransferases in patients with hepatopathies).

Essential congenital liver diseases include the hemochromatosis, Wilson’s disease, α1-antitrypsin deficiency, familial cholestasis, hyper bilirubinemic syndromes, primary porphyries and metabolic disorders (e.g., fatty acid oxidation disorder).

Celiac disease with liver involvement is associated with elevated aminotransferases.

Acute liver failure

Definition: acute liver failure is hepatic damage manifested as jaundice and coagulation disorder with ascites and encephalopathy added as complications within the following 4 weeks. Liver failure can occur as:

  • Acute failure in a previously healthy liver
  • Acute deterioration of a known or unknown chronic liver disease.

The spectrum of chronic liver disease can range from bland steatosis to hepatitis to compensated or decompensated cirrhosis. The acute event can be triggered by: hepatotropic viruses, toxins, sepsis, drugs, esophageal variceal hemorrhage.

The following distinctions are made in terms of progression and the occurrence of encephalopathy:

  • Fulminant liver failure: manifests within a week
  • Acute liver failure: manifests between 1–4 weeks
  • Subacute liver failure: manifests later than 4 weeks afterwards.

The pathophysiology of acute liver failure is similar to that of a systemic inflammatory response syndrome (SIRS). Patients experience immune dysfunction. An adequate response to toxins is no longer possible.

Acute liver failure is caused by alcoholic liver cirrhosis (50–70%), hepatotropic viral hepatitis (15%) and drugs (paracetamol) in Western countries, and by hepatitis infections (70%) and less by alcohol abuse in Asian countries. In the latter, reactivation of a hepatitis B infection results from chemotherapy, immunosuppressive therapy, HIV therapy or rituximab (anti-CD20). Reactivation of chronic hepatitis C due to chemotherapy has also been described. Hepatitis E virus (HEV) superinfection is an important cause on the Indian Subcontinent. Important triggers of the disease besides the infections, alcohol abuse and drugs include sepsis, major surgery and esophageal variceal hemorrhage. The cause of acute liver failure is not detected in 17% of adult patients and about 45% of children. In a study /52/ on children, acute liver failure was caused by the following diagnoses: Drugs 15.8%, autoimmune hepatitis 6.8%, metabolic disorders (e.g. fatty acid oxidation disorder, tyrosinemia, Wilson’s disease) 9.7%, hepatotropic and non-hepatotropic viruses 6.4%, other diagnoses 14.5%, no diagnosis 46.8%.

Various scores are used for the prognostic assessment of the severity of the disease. Some of these scores are listed in Tab. 1.2-2 – Indication criteria for orthotopic liver transplantation in cases of acute liver failure.

Laboratory findings: Organ failures are identified with the use of a modified Sequential Organ Failure Assessment score (the EASL-CLIF consortium organ-failure scoring system. Besides the clinical picture, a bilirubin concentration > 5 mg/dL (85 µmol/L) and INR higher than 1.5 or PT below 40% are important criteria for acute liver failure /53/.

Hepato-renal syndrome (HRS)

HRS is a potentially reversible dysfunction of the kidneys. Type-I HRS is an acute, prognostically unfavorable form associated with rapid impairment of hepatic function. Diagnostic criteria for types I/II are:

  • Liver cirrhosis and ascites
  • Creatinine in serum > 1.5 mg/dL (133 μmol/L) and, in type I, > 2.5 mg/dL (221 μmol/L)
  • No decrease in creatinine after at least 2 days without diuretics therapy
  • No therapy with nephrotoxic agents
  • No shock symptoms
  • No renal parenchymatous changes (normal appearance of the kidneys on ultrasound), proteinuria ≤ 500 mg/24 h, no micro hematuria > 50 erythrocytes/μL.

Table 1.2-6 Hepatitis B states

State

Laboratory result

Acute hepatitis B 

  • HBV DNA positive
  • Anti-HBc IgM positive
  • Anti-HBc IgG negative
  • Anti-HBs IgG negative
  • Anti-HBe IgG negative

Chronic hepatitis B

  • HBV DNA 3+ to 1+/-, up to negative
  • HBsAg positive
  • Anti-HBs negative
  • Anti-HBc positive
  • HBe positive/negative
  • Anti-HBe positive/negative
  • GPT elevated/normal

Hepatitis B be cured

  • HBV DNA negative
  • Anti-HBc positive
  • Anti-HBs positive
  • HBsAg negative
  • GPT normal

Vaccination against hepatitis B

  • Anti-HBs positive, protection if concentration is >100 IU/ml solitary

Table 1.2-7 Assessment of patients with chronic hepatitis B (CHB) based upon HBV and liver disease markers /24/

Marker

HBeAg positive
infection

HBeAg positive
hepatitis B

HBeAg negative
infection

HBeAg negative
hepatitis B

HBsAg

High

High/intermediate

Low

Intermediate

HBeAg

Positive

Positive

Negative

Negative

HBV DNA

> 107 IU/mL

104–107 IU/mL

< 2,000 IU/mL

> 2,000 IU/mL*

ALT

Normal

Elevated

Normal

Erhöht

Liver disease

None/minimal

HBeAg positive

None

Moderate/severe

* HBV DNA can be between 2,000 and 20,000 IU/mL in some patients without signs of CHB.

Table 1.3-1 Principle of ALP determination

4-NPP + X-OH ALP 4-NP + X-OPO 3 H 2

Table 1.3-2 Reference intervals of ALP

Total ALP in serum, plasma; data expressed in U/L (µkatal/L)

(18–49 years) 33–98 U/L (0.55-1.64 μkatal/L) /4/

(≥ 20 years) 43–115 U/L (0.72–1.92 μkatal/L) /4/

Consensus DGKL + VDGH /10/:

Adults 55–105 (0.92–1.75), 40–130 (0.67–2.17)

Children /11/

0–1 yr.

89–370

(1.49–6.3)

89–370

(1.49–6.3)

1–3 yrs.

91–334

(1.52–5.6)

91–334

(1.52–5.6)

4–6 yrs.

97–316

(1.61–5.3)

97–316

(1.61–5.3)

7–11 yrs.

120–340

(2.00–5.7)

110–316

(1.83–5.3)

13–17 yrs.

49–328

(0.82–5.5)

75–363

(1.25–6.1)

Values expressed as 2.5 and 97.5 percentiles.

Conversion: 1 U/L = 0.0167 μkatal/L

DGKL, Dt. Ges Klin Chem Lab Med; VDGH, Verb. Diagnostika- und Gerätehersteller

Bone ALP in serum, plasma

Lectin precipitation /6/

≤ 50

≤ 60

ELISA (U/L) /7/

12–31

15–41

Immunometric assay (µg/l) /12/

3.4–15.0

3.8–21.3

Human placenta ALP (hPLAP) in serum, plasma

ELISA

up to 100 mU/L /13/

Regan-type ALP in serum, plasma

ELISA

up to 100 mU/L /13/

Table 1.3-3 Hepatic and biliary tract diseases possibly associated with elevated total ALP

Clinical and laboratory findings

Acute hepatitides due to primary hepatotropic viruses /29/

The four forms of acute viral hepatitis are associated with the following mean elevations of ALP activity in ascending order of severity: Anicteric: 1.5-fold, typically icteric: 2-fold, cholestatic: 4-fold, necrotizing: 2-fold. In the delayed cholestatic course (week 2 to 3 after occurrence of jaundice), the ALP level becomes elevated. The aminotransferases do not decrease as in the uncomplicated form but remain at a plateau.

Acute hepatitis due to non-hepatotropic viruses

It has been found that 80% of the patients have elevated aminotransferases, 50% have elevated bilirubin and 30% have elevated ALP.

Alcoholic hepatitis

The acute form occurs following acute alcohol intake in chronic alcoholism and indicates severe parenchymal damage. Aminotransferase and GGT can be elevated up to 20-fold and the ALP can be elevated up to 5-fold.

Chronic viral hepatitis

ALP activity is increased 2-fold on average in chronic active hepatitis and remains within the reference interval in the clinically persisting form /29/.

Liver cirrhosis

The elevation of the ALP activity in liver cirrhoses of various etiologies is as follows: viral and cryptogenic form: within the reference interval, alcohol-toxic form: about 1.5-fold and primary biliary form: about 5-fold. The liver ALP and, especially, the intestinal ALP are elevated in portal hypertension or acute right heart failure /30/.

Fatty liver

In alcoholic steatosis and non-alcoholic steatohepatitis, the ALP activity usually remains within the reference interval. However, in pronounced fatty liver with toxic fatty degeneration, there can be strongly elevated ALP and GGT and only mildly elevated aminotransferase /31/.

Hepatic amyloidosis

Liver involvement in collagen disease, Gaucher’s disease. The ALP level can be mildly elevated. The aminotransferases are elevated less often /31/.

Obstructive jaundice

In acute obstruction due to gall stones, the aminotransferases surge within 24 hours (by about 5–20-fold the mean normal level) and decrease again within a week. The ALP is not elevated significantly until after 24 hours and reaches 3–10-fold levels if the stasis persists for several days. Prolonged stasis causes re-elevation of the aminotransferases. Tumor-related, gradual obstructions of the extrahepatic biliary tract (head of pancreas tumor) have high ALP levels at the time of diagnosis. The ALP returns to normal within 10 days after surgical correction of the obstructive jaundice. If the acute obstructive jaundice is complicated by purulent cholangitis, ALP elevation may not occur /32/.

Primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic inflammatory disease of the small and medium biliary tract and, at age 40–60 years, is 6–10 times more common in women than in men. In the catchment area served by a large hospital, the incidence was about 20 and the prevalence was about 120 per million inhabitants /33/. PBC is quite often detected within the scope of routine testing due to elevated ALP, GGT and IgM values. It can also be associated with autoimmune or HBsAg positive chronic active hepatitis (CAH), alcohol-toxic hepatitis or collagen disease. However, IgM primary is not elevated in alcohol-toxic hepatitis. Moreover, PBC can at first manifest as an acute, cholestatic liver disease in which case it resembles CAH. In the immunofluorescence assay, 85% of the patients with PBC are AMA positive and, with additional methods (ELISA, Western Blot), 95% of the cases have antibodies against the E2 subunit of the pyruvate dehydrogenase complex (AMA-M2) /33/. The ALP is already elevated before the onset of clinical symptoms and increases along with bilirubin with increasing duration of the disease.

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease of unknown origin. It is characterized by progressive inflammation with fibrosis and destruction of the intrahepatic and extrahepatic biliary tract. In the USA and Western Europe, a considerable proportion of inflammatory bowel diseases is associated with PSC. The prevalence is 1–4 in 100,000 individuals. About 70% of the cases are men, the average age is 40 years. Clinical symptoms usually occur 1–2 years before diagnosis. Gradually increasing fatigue and itching, followed by jaundice, are common symptoms. About 50–66% of the patients have hyperbilirubinemia at the time of diagnosis, with mildly elevated aminotransferase levels and 2–5-fold elevated total ALP levels /34/.

Ascending infection from the duodenum is a common path of infection. Typical symptoms of cholangitis (PSC) include fever, right epigastralgia, jaundice, elevated ESR and leukocytosis. ALP, GGT and CRP levels are strongly elevated and aminotransferases are mildly elevated /35/.

Intrahepatic cholestasis of pregnancy

Primary intrahepatic cholestasis of pregnancy (ICP) occurs in the last trimester of pregnancy. Bilirubin is elevated more strongly, the ALP is elevated 3–5-fold, and the elevation of the aminotransferases (see Tab. 1.6-4 – Aminotransferases in patients with hepatopathies) can vary. Levels return to normal 2 weeks after delivery /36/.

Purulent liver abscess

Patients with purulent liver abscesses can have elevated ALP and LD as well as fever, leukocytosis, elevated ESR and hypoalbuminemia. Approximately 50% of the blood cultures are positive. The ALP level can be elevated up to 2-fold in chronic amebic abscesses /31/.

Monitoring after orthotopic liver transplantation /37/

The patient’s problems occurring after orthotopic liver transplantation are implications from the pre-existing condition, from surgery and from the immune response to the foreign organ. Approximately 50% of transplant patients show symptoms of rejection reaction. The initial attack in a rejection episode is directed against the biliary tract system. Therefore, elevations of bilirubin, ALP and GGT are indicative biomarkers. The diagnostic sensitivity of increased ALP is 69%, that of GGT is 91% and the positive predictive values are 71% and 68%, respectively.

Phenprocoumon-induced hepatitis /38/

Several cases of phenprocoumon-induced hepatitis have been described in the literature. The first phenprocoumon-induced hepatitis usually has a latency period of several weeks; this period is shorter and the symptoms are more severe if the drug is taken again.

Laboratory findings: Bilirubin and aminotransferases are significantly elevated, ALP is elevated approximately 3-fold and GGT approximately 10-fold.

Primary hepatocellular carcinoma

The elevation of the alpha-fetoprotein is the earliest marker. The ALP levels are usually more strongly elevated than the aminotransferases /31/.

Other liver tumors

Only more severe necroses cause the elevation of aminotransferases, ALP and GGT /31/.

If the bilirubin, aminotransferase, ALP and LD levels are normal, metastases can be ruled out with 98% probability /30/. If metastases are present, some or all of the above-mentioned parameters are elevated, including CEA in many cases; the alpha-fetoprotein is normal or below 100 µg/L.

Drugs can cause liver injury that clinically and diagnostically corresponds to the disease pattern of intrahepatic cholestasis, the hepatitic form or a mixed form of the two. In the cholestatic form, the ALP activity is increased by more than 2-fold, and the aminotransferases are normal. In the hepatitic form, the aminotransferases, in particular, and occasionally the GLD are elevated, but the ALP is normal. In the mixed cholestatic/hepatitic form, the aminotransferases are elevated by more than 2-fold and the ALP is only mildly elevated /22/. See also Tab. 1.6-4 – Aminotransferases in patients with hepatopathies and Section 1.9 – Gamma-glutamyl transferase (GGT).

There is a correlation between elevation of the ALP and liver involvement. In malignant non-Hodgkin’s lymphoma, approximately 40% of the patients with liver involvement have elevated ALP levels. However, ALP elevations without liver involvement are also found /39/.

Table 1.3-4 Diseases of the bone associated with elevated total ALP

Clinical and laboratory findings

Bone fracture /40/

The following total ALP pattern occurs in the first 20 weeks following a fracture of the tibial shaft: The ALP increases continuously during the healing process, but the upper reference limit is only exceed in about 20% of the patients. The bone ALP declines in the first week, reaches a nadir on day 8 and then increases steadily again and reflects the pattern of the total ALP. Osteocalcin increases in the first 4 days, followed by a continuous decline with a nadir in week 5, and then increases again continuously.

Paget’s disease of bone /41/

Paget’s disease is characterized by focal areas of increased but disorganized remodeling of one or several bones. It rarely occurs before the age of 55. Prevalence increases clearly thereafter. 5% of the women and 8% of the men in the 8th decade of life are affected by the disease in some countries. The disease is triggered by pathologic giant osteoclasts with strongly increased resorption activity. The disease preferably affects the axial skeleton, involving the pelvis in 70%, the femur in 55%, the lumbar spine in 53%, the skull in 42% and the tibia in 32% of the cases. The bone tissue produced in a haste as a result of the rapid bone loss is of inferior mechanical quality. This leads to the risk of deformations, fractures, pain and articular and neurological complications. Pathogenesis is believed to be due to the late sequela of a virus infection, possibly Paramyxo virus (e.g., rubeola, RSV).

Laboratory findings: determination of ALP, calcium, 25-hydroxy vitamin D [25 (OH)D], albumin and creatinine. Isolated elevation of the ALP occurs in many cases; however, normal ALP do not exclude Paget’s disease if only a few limited bone areas are involved. Low 25 (OH)D concentrations occurring in many elderly individuals lead to elevated ALP. The ALT should be determined to exclude hepatic ALP elevation. Determination of bone ALP or N-terminal pro peptide may be necessary in liver disease. Bisphosphonates reduce the disease activity; suppression of ALP to the reference interval induces extended remission. The ALP reaches minimum levels after 3–6 months. The ALP should be monitored every 3–6 months and therapy cycles should be restarted if the symptoms increase after temporary improvement. The complication rates in patients with normalizing and non-normalizing ALP are roughly the same.

Osteomalacia

Osteomalacia is subdivided into three groups according to etiological and clinical aspects:

  • Vitamin D deficiency
  • 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25 (OH)2 D] metabolism disorder
  • Renal-tubular-related.

Whereas the total ALP and bone ALP are always elevated, the pattern of calcium and phosphate in serum and urine depends on the cause of the disease.

According to laboratory findings, osteomalacia can be subdivided into a hypocalcemic and a hypophosphatemic form depending on the primary event.

Vitamin D deficiency: – Insufficient exposure to sunlight, malabsorption syndrome (e.g., gluten-enteropathy, Crohn’s disease); – Individuals with dark skin

The initial stage of vitamin D deficiency is characterized by hypocalcemia at normal phosphate concentration. In the second stage, the developing secondary hyper parathyroid disorder leads to normalized serum calcium, hypophosphatemia and elevated ALP. In the third stage, the ALP becomes elevated further along with the developing florid osteomalacia/rickets, and hypophosphatemia and hypocalciuria are present. In vitamin D deficiency, 25(OH)D is low and 1,25 (OH)2 D is mildly elevated or mildly low. Osteomalacia of intestinal origin is often combined with osteitis fibrosa and osteoporosis.

Individuals with dark skin can develop osteomalacia because they do not produce enough vitamin D under North-European conditions.

Chronically ill patients /43/

There is a linear correlation between the decline in 25(OH)D and the elevation of ALP in patients with liver cirrhosis and alcoholism. Those with severe 25(OH)D deficiency (below 12.5 nmol/L) show twice as high ALP levels (150 vs. 76 U/L) compared to those without vitamin D deficiency. These individuals have elevated parathyroid hormone concentrations (median 5.1 pmol/L) compared to 2.8 pmol/L in individuals with normal 25(OH)D.

Vitamin D metabolism disorder

The determination of bone ALP is more sensitive than that of total ALP. Bone ALP can already be elevated even if total ALP is still normal.

– Pseudo vitamin D deficiency rickets types I + II

Two types are distinguished. Both are hereditary and associated with increased ALP activity. Type 1 manifests clinically in the first year of life and is due to a defect of the renal enzyme 25-hydroxy cholecalciferol-1α-hydroxylase; 1,25 (OH)2D is very low. Type II occurs in childhood or sporadically; the end organs do not respond to 1,25 (OH)2D. Pseudo vitamin D deficiency rickets are diagnosed by the detection of hypocalcemia, hypophosphatemia and aminoaciduria.

– Anti epileptic drugs, phenytoin, phenobarbital, primidone, carbamazepine

Long-term treatment with anti epileptic drugs can cause osteomalacia and 1.5-fold elevated ALP. The 25(OH)D concentration decreases due to the induction of microsomal enzymes that cause the production of unphysiological vitamin D metabolites and inhibit the hydroxylation of vitamin D at position 25 to become 1,25 (OH)2/44/. This leads to reduced intestinal calcium absorption which, in turn, results in secondary hyper parathyroid disorder based on the tendency toward hypocalcemia. Moreover, anticonvulsive drugs inhibit the secretion of calcitonin. This leads to increased bone resorption and inhibits renal excretion of calcium and phosphate and, ultimately to an improved balance of the two minerals.

Renal tubular defects – Generally

This group of defects causes rickets/osteomalacia and is characterized by a multitude of syndromes. The defects are hereditary in many cases and can also occur sporadically in adulthood. They are mainly diagnosed based on hypophosphatemia with elevated ALP at normal calcium, PTH and 25(OH)D.

– X-linked phosphate diabetes

Patients have calcifications of the tendons, ligaments and articular capsules besides osteomalacia. Hypophosphatemia can already be detected shortly after birth; clinical symptoms emerge in the first two years of life.

– Phosphate diabetes

Autosomal phosphate diabetes causes mild rickets and mild osteomalacia.

– Oncogenic osteomalacia

In oncogenic osteomalacia, the tumor stimulates phosphaturia and inhibits renal 25-hydroxy cholecalciferol-1α-hydroxylase. Phosphate diabetes disappears and the ALP returns to normal after the tumor has been removed.

– Renal tubular acidosis types I + II

Hereditary disorder of the distal tubule. Type I is characterized by abnormal H+ secretion and type II by abnormal bicarbonate reabsorption. The urine is acidic, and progressive nephrocalcinosis and renal insufficiency develop.

– De Toni-Debré Fanconi syndrome

Autosomal recessive disorder of the proximal and distal nephron. The disorder can develop in childhood or adulthood. Besides rickets, pronounced forms can be manifested as polydipsia, polyuria and anorexia already in childhood.

Renal osteodystrophy /46/

For renal osteodystrophy (ROD), see also Tab. 6.1-6 – Chronic kidney disease mineral bone disorder; diseases involving disruptions of bone metabolism. The total ALP is insufficient to determine the osteoblast activity, whereas the bone ALP correlates well with the bone formation rate and the osteoblast surface. The bone ALP is significantly higher in patients with high bone turnover (ROD type 1) than in patients with normal or low turnover (type 2 and/or adynamic bone disease). Normal or low turnover ROD can be excluded in many cases if the bone ALP is higher than 40 µg/L. Low bone ALP and elevated concentrations of intact parathyroid hormone (iPTH) largely rule out high turnover. Low bone ALP suggests low turnover ROD /47/. Elevated bone ALP at normal iPTH indicate that the causes of the disease are not PTH-related.

The measurement of bone ALP is also important for the monitoring with calcitriol treatment [1,25 (OH)2D]. A decline in bone ALP is a better indicator of adequate response than changes in iPTH. The induction of adynamic bone disease with normal iPTH is a potential problem of long-term calcitriol treatment. Calcitriol treatment should be discontinued if the bone ALP reaches the reference interval (below 20 µg/L). Problems may be encountered in patients where the bone ALP returns to normal under calcitriol treatment and iPTH is in the range of 150–300 ng/L.

Kidney transplantation

It is recommended to determine the bone ALP for assessment of the bone metabolism. The bone ALP declines one week after transplantation, then rises again and reaches pre-transplantation levels after 1 month. This pattern is explained by the effect of the administered glucocorticoids and cyclosporin on osteoblast activity. Glucocorticoids inhibit intestinal calcium absorption, and cyclosporin inhibits the renal 25-hydroxy cholecalciferol-1α-hydroxylase and, thus, can lower the 1,25 (OH)2 D concentration /48/.

Primary hyperparathyroidism

The total ALP is mildly elevated or normal. The bone ALP is elevated more pronouncedly and better reflects changes in the skeletal system /3/.

Osteoporosis

Osteoporosis is a systemic disease characterized by low bone mass, the destruction of the bone micro architecture and an increase in susceptibility to bone fracture. The following WHO definition applies to Caucasian women /49/: A T-score below –2.5 is classified as osteoporosis and a T- score between –1 and –2.5 is classified as osteopenia. The bone density of young, healthy individuals was used for comparison. Accelerated bone loss in the first postmenopausal years is characterized by increased bone turnover compared to premenopausal conditions and shows an imbalance between bone formation and resorption. The total ALP is not suited as an indicator of osteoporosis, and the bone ALP is only suited to a very limited extent. Postmenopausal women have much higher bone ALP levels than premenopausal women, but there is no correlation with the Z-score of bone density.

The treatment of short stature children with growth hormones is expensive. Therefore, it is important to have predictive biomarkers to indicate successful hormone treatment at an early stage. In a study /50/, the bone ALP and the pro collagen-III peptide proved to be good predictors. However, the bone ALP was not a better predictor than the total ALP. Measurements were performed before and 3 months after treatment was started. Treatment was considered to be unsuccessful if the bone ALP did not rise by more than 50 U/L during this period.

Acromegaly causes an elevation of the total ALP due to elevated somatomedin C concentration. It stimulates osteoblast activity which results in increased production of bone ALP. The normalization of the somatomedin C concentration is the most reliable criterion for the assessment of reduced disease activity in acromegalic patients. The sole measurement of bone ALP has a diagnostic sensitivity of almost 100% at 88% specificity and, thus, is of similar significance (see also Section 35.4.5.2.2 – Acromegaly).

Elevations of the total ALP by 30–50% above the upper reference limit and elevated bone ALP in serum and the synovial fluid can occur. A release of bone ALP from the synovial tissue is assumed from an etiological perspective /51/.

Table 1.3-5 ALP as biomarker in malignant tumors and bone metastases

Clinical and laboratory findings

Prostate carcinoma

It is generally assumed that bone metastases occur in 75% of patients with prostate carcinoma and PSA levels above 100 µg/L and are rare in patients with PSA levels below 20 µg/L. Patients with a positive bone scan had a median PSA level of 158 µg/L and those with a negative bone scan had a median PSA concentration of 11 µg/L /52/. 27% of patients with prostate carcinoma stage M0 are assumed to have PSA levels above 100 µg/L /53/. The PSA level is thought to be less reliable as a biomarker for staging than bone ALP. Referring to scintigraphically diagnosed bone metastases and applying a cut-off value above 100 µg/L for PSA and above 19 µg/L for bone ALP, the accuracy of PSA was only 69.2% compared to 84.6% reliability of bone ALP /54/.

Breast cancer

Bone metastases in breast carcinoma are mostly osteolytic. Therefore, the elevation of ALP is usually not as pronounced as in a prostate carcinoma with comparable metastasis. The bone ALP is a more sensitive indicator of metastasis than the total ALP. The bone ALP can also be normal if bone lesion is scintigraphically less extensive /55/.

Osteosarcoma, Ewing’s sarcoma

Mildly to extremely elevated total ALP is found. These diseases affect adolescents, and boys more often than girls. Both tumors metastasize preferably into the lung. The decrease in ALP in osteosarcoma is a criterion for successful treatment.

Multiple myeloma

Patients with multiple myeloma show no, or only a mild, elevation of the total ALP. The bone ALP is rather low because bone resorption processes are predominant /55/.

Paraneoplastic syndrome

Paraneoplastic elevations of ALP are described under hypernephroma. They are thought to occur together with hypercholesterolemia and hypergammaglobulinemia. Hepatosplenomegaly also belongs to this syndrome /56/.

Human placental ALP (hPLAP), an isoenzyme synonymous with the Regan ALP, is expressed in testicular carcinomas (seminoma and non-seminoma testicular carcinomas) and serves as a tumor marker. Its concentration in serum increases with increasing size of the tumor. In a study /57/ (72 seminomas, 33 non-seminomas, 40 mixed tumors), 69% of the tumors were in stage I, 19% were in stage II and 11% were in stage III according to Lugano at the time of diagnosis. The diagnostic sensitivities of hPLAP were 58.8% for seminomas, 44.4% for non-seminomas and 41.7% for mixed tumors at 84% specificity. The combined utilization of hPLAP, hCG and LD increases the diagnostic sensitivity. Applying the cut-off values hPLAP ≥ 100 mU/L, hCG ≥ 5 IU/L and LD above the upper reference limit, the sensitivities in 361 seminoma patients were 74% in stage I and 86% in higher stages compared to patients with non-seminoma tumors. The hPLAP was the only positive tumor marker in 27% of the cases. The combination of hCG and LD shows diagnostic sensitivities of 38% in stage I and 67% in higher stages /58/.

According to other examiners, the sensitivity of the hPLAP for seminoma was 56% before surgery and 51% for the postoperative detection of metastasis /59/. A half-life of the hPLAP of 2.8 days in non-smokers was correlated with a stage higher than I in 67% of the cases. The detection of hPLAP indicates relapse during monitoring with a diagnostic sensitivity of almost 100% at approximately 50% specificity /60/. Biomarker persistence during or after treatment indicates the presence of undetected metastases. The hPLAP is a good biomarker for the assessment of treatment success in patients under chemotherapy. The 34–60% positivity of the hPLAP in smokers and the high intraindividual variation among smokers are disadvantages of the hPLAP /61/. Therefore, the hPLAP cannot be used for diagnostic purposes in these individuals.

Table 1.3-6 Elevated ALP without recognizable hepatobiliary disease or bone disease

Clinical and laboratory findings

Rheumatic disease /62/

Elevations of total ALP are found at an incidence of 8–50% in rheumatoid arthritis (RA) and ankylosing spondylitis (AS) and more rarely in osteoarthritis. Some patients show elevated bone ALP, some have normal total ALP but elevated bone ALP. The elevated total ALP in RA and AS is correlated with the inflammatory activity of the disease and also with the GGT level, but not with the bone ALP level. This supports the hypothesis that the inflammatory response in RA and AS is responsible for the increased formation of the membrane-bound hepatobiliary enzymes ALP and GGT.

Crohn’s disease /63/

Approximately 20% of patients with Crohn’s disease have elevated total ALP. This affects the liver ALP in most cases (84%), but macro ALP can also be present. The ALP elevation is thought to be due to increased inflammatory activity as is the case with rheumatic diseases.

Diabetes mellitus

Some patients with diabetes mellitus type 2 and osteopenia have elevated bone ALP.

Hyperthyreosis /64/

Hyperthyreosis is associated with increased bone turnover due to increased bone resorption. Histomorphometric and laboratory analyses show a reduced trabecular bone volume and negative calcium balance. Hyperthyreosis is 2.5-fold higher in older women with fracture of the femoral neck than in control subjects. The bone ALP can be elevated and is slightly correlated with FT4 concentration.

Transient hyperphosphatasemia

This condition is a benign familiar phenomenon affecting children and adults. In children, transient hyperphosphatasemia preferably occurs from the age of a few months up to 5 years. The total ALP activity can be 5-fold higher than the upper reference limit in adults. Levels usually remain elevated for about 3 months and as long as 20 months in some cases. Elevations by 20–70-fold the upper reference limit of adults have been described. The elevation involves liver and bone ALP; however, children do not suffer liver or skeletal diseases. There is a genetic predisposition to increased expression of tissue-nonspecific ALP /65/.

The pathogenesis of transient hyperphosphatasemia in adults in unknown. The primary route of clearance of ALP from circulation is through the hepatocytes via specific receptors. It is assumed that increased sialylation of ALP in these patients impedes the absorption via the receptors and results in reduced clearance. The total ALP level in patients with chronic liver disease becomes normal again within 3–6 months /66/.

Pregnancy /67/

During pregnancy, placental ALP is passed to the maternal blood. The reference interval of total ALP is 133–418 U/L during the last trimester. High levels are typical during and after delivery, probably due to placental damage. The half-life of the decrease in placental ALP after delivery is 4–7 days; the total ALP can be expected to have returned to normal after six half-lives (i.e., 4–6 weeks after delivery). In damage of the placenta resulting, for example, from placental infarction, the total ALP and alpha-fetoprotein concentration surge within a day whereas hCG decreases significantly.

Table 1.3-7 Diseases associated with low ALP levels

Clinical and laboratory findings

Various diseases

Hypophosphatasemia is a rare disease and, according to a study /68/, occurs in approximately 0.2% of elderly people. The most common causes are: Condition following cardiopulmonary bypass surgery, protein malnutrition, magnesium deficiency, hypothyreosis and severe anemia.

Wilson’s disease

Hypophosphatasemia in Wilson’s disease, especially fulminant hepatopathy and hemolytic anemia, is believed to be based on low bone ALP levels. According to a study /69/, the stability of bone ALP in plasma is reduced, supposedly as a result of the increase in reactive oxygen due to ceruloplasmin deficiency. Half-life is shortened from 22–66 hours to approximately 6 hours.

HYpophosphatasia (HPP) /70/

Hypophosphatasia (OMIM 146300, 241500, 241510) is a rare, inherited metabolic disorder that arises from loss-of-function mutations in the gene that encodes the tissue-nonspecific isoenzyme of ALP (TNSALP). As a result of these mutations as many as 260 genetic mutations have been associated with HPP. HPP is associated with a deficiency of liver/bone/kidney ALP. The incidence of the disease has been estimated at 1 case per 100,000 live births. TNSALP is a phosphoisomerase of 507 residues and is anchored at its caboxyl terminus to the plasma membrane by a phosphatidylinositol-glycan moiety. Common clinical features of HPP are defects in bone and tooth mineralization along with the biochemical hallmark of decreased serum ALP. The types of HPP include perinatal (lethal), infantile, childhood, and adult. Two other forms include odontohypophosphatasia (only dental manifestation and decreased ALP) and pseudohypophosphatasia. The latter is clinically indistinguishable from the infantile HPP, but serum ALP is normal. HPP manifests in numerous ways. The most severe forms of disease have an autosomal recessive mode of inheritance. Compound heterozygosity and autosomal mutations in the TNSALP gene may cause childhood and adult HPP. The perinatal HPP, the severest form, is almost universally fatal shortly after birth. The adult form may manifest with recurrent or slow-to-heal metatarsal fractures or subtrochanteric femoral pseudo fractures or can also occur without any symptoms. The perinatal and infantile HPP have an autosomal recessive mode of inheritance, whereas the juvenile and adult forms have an autosomal dominant mode of inheritance and an autosomal recessive mode of inheritance, respectively. Heterozygous carriers of the severe form are usually clinically normal or have small or no skeletal changes and a moderate decrease in ALP.

Laboratory findings: the hallmark of laboratory finding in HPP is a low activity of ALP. However, a low ALP is not pathognomonic as this finding can be associated with different diseases. Additional findings that are supportive in the diagnosis of HPP are:

Hypercalcemia, hyper phosphatemia and hypercalciuria, particularly in the infantile and childhood form

Elevated substrates of ALP, e.g., phospho ethanolamine and pyridoxal 5’phosphate a product of vitamin B6. Patients taking supplements containing vitamin B6 should discontinue them 2 weeks prior to measurement.

Molecular analysis of mutations in ALP /71/.

Corticosteroid-induced osteoporosis /72/

Corticosteroid-induced osteoporosis is a loss of bone caused by reduced bone formation in relation to bone resorption. The reduction in bone formation is thought to be due to the direct inhibitory effect of corticosteroids on osteoblasts. Increased bone resorption is based on decreased enteral calcium absorption and increased renal excretion of calcium leading to the development of secondary hyperparathyroidism. Loss of bone is especially pronounced in the first 6–12 months after treatment is started and becomes slower during chronic therapy. This was shown in histomorphometric studies with the daily administration of 10–25 mg of prednisone. The loss of bone resulted in lower bone ALP and osteocalcin concentration, especially in patients with an increased risk of fracture.

Table 1.4-1 Reference intervals of amylase

Reaction temperature at 37 °C

Serum

Urine*

IFCC method; subjects > 17 yrs.

31–107 /1/ (0.42–1.71)

≤ 460 (≤ 7.7)

G3-CNP method; adults /2/ [2-chloro-4-nitrophenyl-α-D-maltotrioside and potassium thiocyanate] /3/

30–90 (0.50–1.5)

25–98 (0.42–1.0)

Vitros method; adults [amylopectin reacton red 2B]

30–110 (0.50–1,83)

≤ 640 (≤ 0.7)

Pancreatic amylase (EPS-G7-NP method with 2 antibodies to salivary amylase)

Adults /4/

13–53 (0.2–0.9)

≤ 640 (≤ 9.8)

Children /5/:

< 1 year

0–8 (0–0.13)

1–9 years

5–31 (0.09–0.52)

10–18 years

7–38 (0.11–0.65)

Data are expressed in U/L (μkatal/L); values are 2.5th and 97.5th percentiles; * Random specimen

Table 1.4-2 Causes of pancreatogenic hyperamylasemia

Clinical and laboratory findings

Acute pancreatitis

Acute pancreatitis: hyperenzymemia over 3 × URL (upper reference limit) from 5–6 hours after the onset of symptoms in most cases, duration: 2–6 days. Maximum values (up to 20 × URL) are observed (no prognostic significance) in serous inflammation.

Chronic pancreatitis (recurring, obstructive)

Recurring chronic inflammation: hyperamylasemia on the day of onset of the disease; duration: 4–6 days to several weeks (in obstructive form and alcoholism-related recurrences), increase again in the event of abscess and/or pseudocyst formation. Normal concentrations of α-amylase and P-amylase in symptom-free intervals. Hyperenzymemia in alcohol-induced forms only in approximately 60% of the patients, often with simultaneously elevated S-amylase.

Acute abdomen

Elevation of α-amylase 5–6 hours after the onset of the symptoms involving the pancreas (cholecystitis, penetrating duodenal ulcer below 3.5 × URL), duration: 2–4 days (may vary depending on cause and treatment), P-amylase relatively more elevated. Mildly (below 2 × URL) and inconsistently elevated concentration in tubal rupture, (elevated S-amylase), peritonitis due to ulcer perforation, ileus, mesenteric infarction, splenic vein thrombosis.

ERCP

Maximum after 6 hours (2–4 × URL) with decline in hyperenzymemia in 2–4 days after uncomplicated surgery.

Table 1.4-3 Causes of extrapancreatic hyperamylasemias

Clinical and laboratory findings

Renal insufficiency

α-amylase (P-amylase > S-amylase) is elevated in cases of glomerular and tubular damage if creatinine clearance falls below 50 [mL × min–1 × (1.73 m2)–1], and is 3 times × the URL in dialysis patients.

Malignant tumor

All isoenzymes are detected. S-amylase is characteristic of well differentiated neoplasms and X-amylase is characteristic of dedifferentiated neoplasms: lung (adenocarcinomas), colon, thyroid, ovary, prostate, cervix and multiple myeloma.

Alcoholism

S-amylase is elevated in 10% of patients with acute ethyl alcohol intoxication; after 5 years of abuse: α-amylase is normal, but the quotient of S-amylase/P-amylase is 1.8 (1.0 in healthy patients); in liver cirrhosis or chronic hepatitis, there are also mildly (below 2 × URL) elevated α-amylase levels (total).

Hepatopathy

Inconsistent increase 1.5–8 times the URL in acute liver congestion, viral hepatitis, liver cirrhosis, hepatocellular carcinoma, liver metastases and liver resection.

Parotitis

Elevation of α-amylase up to 3 × URL (after surgery) or up to 5 × URL (viral infection, mumps; in postprandial sialolithiasis) exclusively due to S-amylase; P-amylase and lipase are only elevated in pancreatic involvement (epidemic parotitis).

Anomaly in 2% of inpatients with permanently elevated α-amylase. Exclusion of AIDS, lymphomas and myelomas required. Pseudo-macroamylasemia due to hydroxy ethyl starch (HES) simulating pancreatitis (often after surgery).

Occasional elevation of α-amylase 2–3 times the URL in regional enteritis and ulcerative colitis, salpingitis, AIDS and diabetic ketoacidosis: Synchronous patterns of α-amylase, P-amylase and lipase in pancreatic involvement.

Table 1.5-1 Angiotensin converting enzyme reference intervals

Method of determination

Reference interval

Lieberman /2/

10–135

Neels et al. /3/

115–420

Ryan et al. /4/

44–138

Silverstein et al. /5/

12–152

Holmquist et al. /6/

8– 52

30–170 /7/

Data expressed in U/L. 1 U is defined as the quantity of enzyme hydrolyzing 1 μmol of substrate per second. Values are x ± 2 s.

Table 1.5-2 Elevated ACE at other diseases and conditions

Clinical and laboratory findings

Chronic berylliosis

Chronic berylliosis is an important differential diagnosis of sarcoidosis. The clinical manifestations of both diseases are identical /8/. ACE levels may be mildly elevated. Differentiation from sarcoidosis based on the beryllium lymphocyte transformation test or a skin test.

Morbus Gaucher

Three-fold elevated ACE levels are measured on average. The Gaucher cell is the source of the SACE activity /9/. Like the epithelioid cells in sarcoidosis, the Gaucher cell originates from circulating monocytes transformed from phagocytic cells to stationary, storing and secretory cells.

Diabetes mellitus

In a study /20/, the SACE values in diabetics with proliferative retinopathy were on average 50% higher than those in healthy control subjects.

Mixed connective tissue disease (MCTD)

MCDT is a disease entity with a high antibody titer against nuclear ribonucleic protein and a combination of the clinical symptoms of progressive systemic sclerosis, polymyositis, and systemic lupus erythematosus. The development of pulmonary hypertension is a major clinical problem of this disease. According to a study /21/, MCTD patients developing pulmonary hypertension have elevated SACE values.

HIV infection

The SACE values in AIDS patients and patients in an intermediate stage of HIV infection are on average 60% higher than those in healthy control subjects /22/.

According to a study /9/, the SACE values in 18 of 20 patients with chronic fatigue syndrome were higher than 35 U/L (measured with the Lieberman method).

The SACE values increase from the 7th month of pregnancy, decrease after delivery and are normal again 6 weeks postpartum.

Table 1.6-1 ALT and AST reference intervals

Serum, plasma
U/L (μkatal/L)

AST

ALT

IFCC method

Adults (reagent without PyP substitution) /3/

< 31 (0.52)

< 34 (0.56)

< 35 (0.58)

< 45 (0.74)

Consensus for upper reference limits (with PyP substitution) /4/

< 35 (0.60)

< 35 (0.60)

< 50 (0.85)

< 50 (0.85)

Children /5/

Age

AST without PyP

AST with PyP

0–1 yr.

16–58 (0.27–0.96)

14–77 (0.24–1.29)

1–3 yrs.

16–60 (0.27–1.0)

19–71 (0.32–1.19)

4–6 yrs.

14–49 (0.24–0.81)

15–53 (0.25–0.89)

7–12 yrs.

16–42 (0.27–0.70)

19–48 (0.31–0.80)

13–17 yrs.

13–38 (0.22–0.64)

15–41 (0.25–0.69)

 

ALT without PyP

ALT with PyP

0–1 yr.

5–41 (0.09–0.68)

4–49 (0.07–0.82)

1–3 yrs.

8–28 (0.14–0.47)

7–29 (0.11–0.49)

4–6 yrs.

6–29 (0.10–0.49)

5–39 (0.08–0.65)

7–12 yrs.

8–36 (0.13–0.60)

7–44 (0.12–0.73)

13–17 yrs.

7–37 (0.12–0.62)

8–45 (0.13–0.75)

Values are 2.5th and 97.5th percentiles. The intervals of aminotransferases with and without pyridoxal-phosphate (PyP) are shown.

Table 1.6-2 ALT activities in serum and their frequency (%) in hepatobiliary diseases, modified from Ref. /9/. ALT values refer to time of admission to hospital

ALT activity (U/L)

< 50

50–200

200–400

400–1000

1000–2000

> 2000

Proportion (%) of patients with corresponding ALT activities

Fatty liver of different etiology

25

72

3

0

0

0

Metastatic liver

35

55

8

2

0

0

Biliary tract obstruction

14

61

14

11

0

0

Cirrhoses other than primary biliary cirrhosis

14

70

10

5

0

0

Toxic liver injury*

19

42

17

19

3

0

Chronic hepatitis

1

42

40

13

4

0

Cholangitis and primary biliary cirrhosis

0

64

20

8

8

0

Acute viral hepatitis

0

0

0

9

34

57

Acutely impaired hepatic blood flow

0

0

0

0

19

81

* Drug-induced, only

Table 1.6-3 Aminotransferases in patients with hepatopathies (see also Tab. 1.2-5 – Biomarkers in hepatopathies)

Clinical and laboratory findings

Acute viral hepatitides due to hepatotropic viruses

Many types of viruses in systemic infection can also affect the liver. However, the clinical picture in hepatotropic viral infection is dominated by the liver disease. The distinction of the hepatitis types A–E is based on immunology and molecular biology. Aminotransferases are normal during the incubation period, but rise sharply in the prodromal stage before bilirubin increases a week later. ALT rises to peak levels of 20–30-fold and AST 10–20-fold the upper reference limit at the onset of jaundice and in the first week of the disease. If the ALT is more than 20-fold and the AST is more than 10-fold the upper reference limit in the differentiation between acute viral hepatitis and intrahepatic and extrahepatic cholestasis, the positive predictive value for acute viral hepatitis is 78% and the negative predictive value that excludes viral hepatitis is 99% /11/. The different progressions of acute hepatitis range from anicteric to typically icteric and cholestatic to necrotizing depending on their severity and are characterized by rising values with reference to the peak levels of the aminotransferases. The cholestatic progression can be distinguished by a multiple increase in GGT and ALP, and the necrotizing progression can be distinguished based on a De-Ritis ratio above 1 and high GLD levels. Anicteric hepatitides are more common in children than in adults. Icteric courses of the disease heal better than anicteric ones.

– Hepatitis A /22/

In 20–30% of adults and 90% of children under 5 years of age with hepatitis A icterus does not occur. The symptomatic course lasts for 3–6 weeks, is benign, self-limiting and does not progress into the chronic state; therefore, there are no chronic virus carriers. The ALT is 20–30-fold elevated, the De-Ritis ratio is about 0.5; levels usually decline again within 6 weeks. About 5–10% of the patients experience protracted or intermittent courses, especially adults, with elevated aminotransferases and persistence of HAV-IgM for as long as one year. Severe courses with sharply elevated enzyme levels, cholestatic forms with high aminotransferases, elevated ALP and GGT and bilirubin above 12 mg/dL (205 µmol/L), partly for several months, occur with increasing age. The mortality rate is 1.1% in patients older than 40 years of age and 0.1% in patients younger than 14 years of age. Infected contacts can be identified already 1–2 weeks before the increase in aminotransferases by examining the stool for hepatitis A antigen.

– Hepatitis B /1322/

Acute hepatitis B infection goes unnoticed by about two thirds of the patients because jaundice does not occur. Therefore, mild forms are often mistaken for common colds, polyarthritis or gastrointestinal complaints. Mildly icteric forms are associated with bilirubin concentrations of up to 5 mg/dL (85 µmol/L); in severe forms, bilirubin can exceed 30 mg/dL (510 µmol/L). Aminotransferases are already elevated at the onset of jaundice and reach a peak level (ALT about 40-fold elevated, AST about 30-fold elevated) a week after the onset of jaundice. The AST/ALT ratio is initially around 0.7 and decreases with increasing healing and decline in aminotransferases. The aminotransferases reach normal levels after 6–12 weeks; ALT and GGT are the last enzymes to return to normal.

Early cholestatic courses develop in approximately 5% of the patients. These patients already have elevated bilirubin at the beginning of the disease, plateau-like strong elevations of aminotransferases for 4–6 weeks, and ALP and GGT activities rise 5–7-fold with peak levels reached 4–6 weeks after the onset of jaundice. Early cholestatic forms are clinically characterized by severe pruritus that does not occur in late cholestatic forms. The latter show elevated ALP, GGT and bilirubin and decreasing aminotransferases.

Fulminant courses have high aminotransferases, an AST/ALT ratio much higher than 1 and a pronounced increase in GLD. A rapid decline in aminotransferases and continued rising of bilirubin, GLD and LD are poor prognostic signs.

The aminotransferases are insignificant for prognostic assessment of acute hepatitis B. The infection is chronic in all perinatally infected children, in 20–50% of individuals infected at 1–5 years of age and in 5% of infected adults.

– Hepatitis C /2324/

During the prodromal phase, the symptoms of acute hepatitis C are similar to those of hepatitis B, albeit not as pronounced. The course of the disease is usually asymptomatic or characterized by non-specific clinical symptoms. 30–70% of the patients have an anicteric course. In the symptomatic course, ALT is elevated up to approximately 15-fold the upper reference limit.

Aminotransferases decrease quickly and return to normal after 5–12 weeks. However, the aminotransferase level is not a prognostic criterion for the elimination of the virus. In patients with consolidation, the ALT levels are initially high and decrease rapidly. Episodic or plateau-like elevations of the ALT are often associated with the transition to the chronic course. The prevalence of fulminant courses is under 1%. Up to 85% of the patients develop chronic hepatitis and 5–25% develop liver cirrhosis.

– Hepatitis D /2526/

Hepatitis D is not an autonomous disease. It is obligatorily associated with hepatitis B and occurs in two forms:

  • As superinfection of HBsAg carriers with the delta virus, where activation of the infection in asymptomatic HBsAg carriers or superinfection with the delta virus in active hepatitis B infection are possible. The course of the disease is severe in most cases; aminotransferases are elevated approximately 20-fold or higher, and the transition to fulminant hepatitis is possible. The virus is not eliminated in 70–90% of the cases, and the disease manifests as chronic progredient severe hepatitis with rapid transition to liver cirrhosis.
  • As co-infection with hepatitis B and delta virus. Hepatitis D follows hepatitis B after a period of 2–4 weeks. The clinical picture of hepatitis D and the aminotransferase course correspond to those in acute hepatitis B. Some patients experience a two-phase course with dual-peak ALT elevation within several weeks. The virulence of the hepatitis B virus is decisive for the pathogenicity of the delta virus infection. If it is low, the delta virus can be eliminated. Approximately 95% of the cases are cured, less than 5% progress into a carrier state and less than 1% develop fulminant hepatitis.

– Hepatitis E /27/

Hepatitis E is the most common form of acute hepatitis in developing countries in Asia, Africa and South and Central America. The virus is excreted in feces and transmitted by fecal/oral route. Hepatitis E patients in industrial countries have a history of travel. Hepatitis E is a self-limiting disease with an incubation period of 2–9 weeks. The clinical course is characterized by jaundice, hepatomegaly and elevated aminotransferases with peaks as in hepatitis A and B. Anti-HEV-IgM can already be detected before the aminotransferases reach peak levels. The ALT and AST return to normal within 6 weeks. Some cases show a cholestatic form with more pronounced increases in GGT and ALP. Mortality is 0.5–4%; pregnant women can develop a fulminant form; therefore, mortality in pregnant women can be as high as 20%.

Hepatitides due to non-hepatotropic viruses

Liver involvement can occur within the scope of systemic viral infections. For example, this is the case in infections with herpes group viruses (herpes simplex virus, varicella zoster virus, Epstein-Barr virus and cytomegalovirus), enteroviruses (Coxsackie virus and ECHO virus), Adeno virus, Rubella virus and viruses that are exotic in our region, such as the Yellow fever virus and the Dengue virus.

– Cytomegalovirus

Approximately 60% of the population are CMV seropositive by the time they reach adulthood. Acute infection starts with uncharacteristic prodromes and can manifest in clinical symptoms such as hepatitis, myocarditis, polyradiculitis and bronchopneumonia. Some adolescents and adults develop hepatitis. The AST and ALT can reach peak levels as high as 15-fold the upper reference limit within the first week of the disease, and the bilirubin concentration can become as high as 7 mg/dL (120 µmol/L) /28/.

Cholestatic forms with 10-fold elevated ALP and 30-fold elevated GGT can occur. CMV infections occur in 20–60% of cases after organ transplantation, mostly within the first 3 months. Elevated bilirubin and aminotransferases are detected besides leukocytopenia and thrombocytopenia. CMV hepatitis is the most common hepatitis not caused by hepatotropic viruses (approximately 1% of hepatitides).

– Epstein-Barr virus (EBV)

The EBV infection is an endemic disease and affects 60–70% of the population up to 20 years of age. The EBV regularly causes hepatitis with aminotransferases elevated up to 5-fold the upper reference limit in the second to fourth week of the disease. Hyperbilirubinemia occurs in approximately 5% of cases /29/. Contrary to the hepatitides with hepatotropic viruses, the elevation of the LD in EBV hepatitis is high in relation to the ALT. Fulminant hepatitis with pronounced bilirubin and aminotransferase elevations and disseminated intravascular coagulation occurs in 1 in 3,000 cases.

– Herpes simplex virus

Hepatitis with elevated aminotransferases as in infection with hepatotropic viruses can occur in immunosuppressed children and adults within the scope of a generalized infection /30/. Patients can experience severe hyperbilirubinemia and massive impairment of the hepatic function with significantly extended prothrombin time. Neonatal herpes has a high mortality.

– Varicella zoster virus (VZV)

About 15–75% of varicella infection cases in children can be associated with concomitant hepatitis with approximately 2-fold elevated ALT /31/. Fulminant courses with high aminotransferases can be a frequent occurrence in immunosuppressed patients.

– Rubella virus

Rubella infections in adulthood can cause anicteric hepatitis with peak aminotransferase levels around 10-fold the upper reference limit /32/. The LD elevation is also relatively pronounced, as in EBV infections.

– Enteroviruses

Coxsackie virus and ECHO virus can cause a severe septic clinical picture in neonates that includes hepatitis, hepatocellular necrosis and high aminotransferases. Hepatitides with high aminotransferases can also occur sporadically within the scope of generalized Coxsackie virus infections in adults /33/. The AST is higher than the ALT in most cases.

– Adenoviruses

Feverish conditions can occur in neonates and immunosuppressed children and adults within the scope of generalized hepatitis, enteritis or pneumonia. Aminotransferases are elevated as in infections with hepatotropic viruses /34/, the elevation of the LD is high in relation to the ALT, and the De-Ritis ratio is higher than 1. Moreover, jaundice is present in many cases and primarily suggests infection with hepatotropic viruses.

Acute co-reaction of the liver in infections

An acute inflammatory co-reaction of the liver can occur in bacterial and parasitic diseases, usually resulting in non-specific reactive hepatitis, partly with cholestasis or only focal damage such as liver abscess.

– Leptospirosis

The leptospiremic phase (stage 1 of the disease) is characterized by fever up to 39 °C, nausea, vomiting, headache and neck pain. In stage 2, the organ manifestation, specific IgM antibodies can be determined serologically and aminotransferases are elevated up to peak levels that are about 5-fold the upper reference limit. The ALP is also elevated, and hyperbilirubinemia is severe in relation to the aminotransferases and reaches values as high as 30 mg/dL (513 µmol/L) /35/. The aminotransferases usually return to normal after 4 weeks and bilirubin returns to normal after 6 weeks. The CK is elevated due to myositis, and necrosis of the renal tubules leads to hematuria, proteinuria and cylindruria.

– Brucellosis

The clinically apparent course of brucellosis (90% of cases are inapparent) is characterized by intermittent fever up to 40 °C. Hepatomegaly occurs in the generalization stage. Aminotransferase and ALP levels are elevated up to 2-fold, hyperbilirubinemia is rarely present /36/. Pronounced elevations in aminotransferases and ALP have been observed in individual cases.

– Q fever

The Q fever is a rickettsiosis that can also occur in Europe. The pathogens of the Q fever are Coxiellaceae that are transmitted from animals to humans. Hepatitis can occur in acute Q fever. Peak aminotransferase levels approximately 10-fold the upper reference limit are reached around day 10 after the increase in body temperature /37/. The De-Ritis ratio is below 1, the ALP is also elevated. The degree of hyperbilirubinemia, if any, is mild with values below 5 mg/dL (85 µmol/L).

– Toxoplasmosis

Toxoplasmosis is a protozoan disease caused by infection with Toxoplasma gondii, with cats as final host and humans as intermediate host. Humans are infected by oral ingestion of oocysts from cat feces via smear infection, oral ingestion of bradyzoites from raw or under cooked meat or they are already infected in utero. The connatal form is distinguished from the postnatal and reactive forms. The latter occurs in immunosuppressed patients. About half of the children with connatal toxoplasmosis present with hepatomegaly and have elevated ALT, GGT and LD levels approximately 5-fold the upper reference limit /38/. This can already be the case in the umbilical cord blood. Inconsistent information is available on liver involvement in postnatal toxoplasmosis. Inflammatory reactions corresponding to hepatitis or cholangitis do usually not occur. Therefore, elevated ALT and other liver enzymes are rather an exception. This also applies to reactive toxoplasmosis in AIDS patients. However, individual cases of severe hepatitides with elevated aminotransferases by 50-fold the upper reference limit have been reported in such patients.

– Echinococcosis

The genus Taenia echinococcus includes two parasites, E. granulosus and E. multilocularis that are pathogenic for humans. The first is the three-segmented dog tapeworm and causes cystic echinococcosis; the latter is the five-segmented fox tapeworm and causes alveolar echinococcosis. As intermediate host, humans are infected by oral ingestion of tapeworm eggs through direct contact with animals or ingestion of contaminated food or water. The prevalence of echinococcosis in Germany is 1.6 in 100,000 inhabitants, two thirds of these being migrants. The proportion of liver involvement in cystic echinococcosis is 65%, whereas alveolar echinococcosis is limited to the liver in almost all cases. The echinococcus cysts are usually located in the right hepatic lobe where they often grow for years without causing any symptoms.

According to a study /39/, elevated levels occurred in the following proportion of patients with cystic echinococcosis: bilirubin in 50%, GGT in 50%, ALP in 26%, ALT in 30%, AST in 18%. Most patients with alveolar echinococcosis are reported to have elevated ALP and GGT and polyclonal gammopathy. Eosinophilia is said to occur in 20–50% of patients with echinococcosis.

Liver abscess (pyogenic, amebic) /40/

Liver abscesses have an incidence of approximately 10 in 100,000 hospitalizations. In the industrialized Western countries, 80% of liver abscesses are pyogenic. Common pathogens include staphylococcus, streptococcus, enterococcus, coliform bacteria and other gram-negative rods. The pathogens invade the liver via the following pathways: The canalicular route in cholecystitis, the hematogenous route via the portal vein or hepatic artery, and germs spreading from abscesses, tumors or perforation of neighboring organs.

About 10% of liver abscesses are caused by the ameboid trophozoites of Entamoeba histolytica. In amebic dysentery, the amebas penetrate the intestinal wall and enter the liver via the portal vein. This leads to hepatocytolytic necrosis. The pathogens tend to be located at the periphery of the abscess; the cytolytic, yellowish to brown content of the cyst is usually free from parasites. No cause has been found for 90% of liver abscesses; they are referred to as cryptogenic liver abscesses.

Clinical aspects: The course of the disease is clinically normal or accompanied by symptoms such as abdominal pain, fever and jaundice.

Laboratory findings: the focus in liver abscesses is on biomarkers of inflammation. Neutrophilic leukocytosis is present, and CRP and BSR are elevated. It is mainly the cholestatic enzymes GGT and ALP that are elevated; the ALT shows pathological activity in about half of the cases /41/. Aminotransferases are usually normal in amebic liver abscess /42/. Significantly elevated antibody titers against amebas are measured in the first two weeks of the disease. Peak levels are reached in the second to third month after the onset of the disease; titers can remain elevated for one year and longer.

Chronic viral hepatitis (CVH) due to hepatotropic viruses /43/

Chronic viral hepatitis is an inflammatory disease of more than 6 months’ duration. More than 500 million individuals worldwide suffer from CVH. CVH is based on infection with the hepatitis B virus, hepatitis C virus or hepatitis D virus. It causes severe complications such as liver cirrhosis and hepatocellular carcinoma. CVH prognosis depends on the progression of fibrosis, which varies in individual patients. Fibrosis is influenced by factors such as gender, age, alcohol consumption and immune status. The assessment of the severity of liver disease is important to identify patients for treatment and hepatocellular carcinoma (HCC) surveillance. It is based on a physical examination and laboratory parameters.

Laboratory investigations: the biochemical markers ALT, AST, GGT, ALP, bilirubin serum albumin and gamma globulins, prothrombin time and blood count are recommended in all patients. Severe inflammation of the liver is associated high ALT levels. In cases where biochemical and hepatitis markers reveal inconclusive results a non-invasive test or a liver biopsy should be performed to determine disease activity.

– Hepatitis B /4344/

About 350 million individuals worldwide suffer from chronic hepatitis B (HBV) infection. The prevalence is high in Southeast Asia and in the sub-Saharan region, where more than 8% of the population are chronic HBsAg carriers. The infection is transmitted perinatally or in early childhood. In the industrial countries, the prevalence is below 1% and infections mainly occur in high-risk groups such as drug addicts and persons with multiple heterosexual partners. Chronic HBV infection is a dynamic process with an immune tolerance phase and an immune clearance phase followed by an inactive carrier phase when hepatitis is in remission. See Tab. 1.2-5 – Biomarkers in hepatopathies.

Perinatal infection

Perinatal infection is characterized by minimal liver injury, an extended immune tolerance phase with HBeAg positivity, high HBV DNA concentration and low HBeAg clearance. The ALT is normal.

Chronic HBV infection in childhood and adulthood

The initial evaluation of a patient with chronic HBV infection should include a complete history, a physical examination, biochemical markers for the activity of liver disease and severity markers of HBV infection /44/. See Tab. 1.2-5 – Biomarkers in hepatopathies.

Severity markers of HBV infection

HBeAg and anti-HBe detection are important for the determination of the phase of chronic hepatitis B infection.

Measurement of HBV DNA serum concentration is important for the diagnosis, establishment of the phase of infection, the decision to treat and subsequent monitoring of patients.

Serum HBsAg quantification can be useful, particularly in HBeAg-negative chronic HBV infection and in patients to be treated with interferon-alpha. See Tab. 1.2-7 – Assessment of chronic hepatitis B.

HBV genotype is not necessary in the initial evaluation, although it may be useful for selecting patients to be treated with interferon-alpha offering prognostic information for the probability of response to interferon-alpha therapy and the risk of hepatocellular carcinoma.

Co-morbidities, including alcoholic, autoimmune, metabolic liver disease with steatosis or steatohepatitis and other causes of chronic disease should be excluded including co-infections with hepatitis D virus and hepatitis C virus and Hi virus.

Testing for antibodies against hepatitis A virus (anti-HAV) should be performed, and patients with negative anti-HAV should be advised to be vaccinated against HAV.

Activity forms of chronic hepatitis B

Low-activity, moderate-activity and high-activity forms are distinguished. In the low-activity form, the aminotransferases are 2–4-fold elevated, with a De-Ritis ratio below 1 and mildly elevated GGT. In the moderate-activity form of disease, the aminotransferase levels are the same as in the low-activity form, but GGT is higher and CHE is near the lower reference interval value. The high-activity form shows aminotransferases 5–10-fold the upper reference interval value. The ALT is higher than the AST in the beginning, but the activity of both enzymes declines with increasing cellular necrosis; the De-Ritis ratio is higher than 1 and increases continuously. The GGT is 5–10-fold elevated, CHE and albumin levels are low, the prothrombin time decreases below 70% and the IgG concentration in serum increases. The bilirubin can increase to 20 mg/dL (340 µmol/L) in some cases. Recurrent necrotic episodes with high GLD can also occur.

Therapy /13/: See Tab. 1.2-5 – Biomarkers in hepatopathies.

– Hepatitis C /1443/

The prevalence of chronic hepatitis C (HCV) infection is 3% with a fluctuation range of 0.1–5%. There are 150 million HBV carriers worldwide, including 5 million in Western Europe and 4 million in the USA. In the industrial countries, HCV causes 20% of acute hepatitides, 60% of chronic hepatitides, 40% of terminal liver cirrhosis, 60% of hepatocellular carcinoma and 30% of orthotopic liver transplantations. The incidence of new symptomatic infections is 3/100,000 individuals per annum.

The following findings apply to patients with chronic HCV infections:

  • About 25% of the cases have no elevated ALT despite the presence of detectable HCV RNA in serum. Histological changes in the liver are small, and transition to cirrhosis is rare.
  • About 50% of the cases suffer from mild liver disease with HCV RNA detectable in serum and mildly elevated, fluctuating ALT. The ALT fluctuations often range between normal and 5-fold the upper reference limit. Histology shows mildly necrotic and inflammatory changes and no or mild fibrosis. Progression toward cirrhosis is slow or does not develop in many patients.
  • About 25% of the cases have moderate to severe chronic hepatitis. The ALT is generally higher than in the mild form of chronic hepatitis. However, the ALT is not a good prognostic factor on an individual basis. Drug abuse should be considered in patients with ALT levels more than 10-fold the upper reference limit /45/. In a study /46/, the following details on the relation between the predictive value of ALT and the histological findings are presented: according to the METAVIR score system, patients with normal ALT for 6 months in serial assay show a score of F1 in 65% of cases and a score of A1F1 in 26% of cases (i.e., 26% have moderate chronic hepatitis). Patients with elevated ALT have a score of at least F1 in 99% of cases and a score of at least A1F1 in 88% of cases. The latter cases cannot be classified as mild or non-progressive hepatitis /46/.

15–25% of patients with anti-HCV have no HCV RNA. If such patients have elevated ALT, they should be examined carefully to exclude possibly incorrect diagnostic findings (see Section 1.2 – Biomarkers of liver disease).

Therapy /14/: See Tab. 1.2-5 – Biomarkers in hepatopathies.

NAFLD and NASH /4748/

The non-alcoholic fatty liver disease (NAFLD) is the most common cause of liver diseases in children and adolescents and has a prevalence of about 3% at 2–19 years of age. The prevalence is 10–15% in normal-weight adults and 70–80% in overweight adults. The spectrum of NAFLD ranges from simple and reversible steatosis to non-alcoholic steatohepatitis (NASH). NAFLD is associated with insulin resistance, diabetes type 2 and the risk of atherosclerosis.

Laboratory findings: the liver enzymes are generally not suited as biomarkers for diagnosing NAFLD. Initially, the ALT is mildly elevated and higher than the AST; the ratio is reversed upon transition to NASH. The ALT is 1.5–2-fold elevated, depending on the fatty liver index. However, the aminotransferase levels can only be used to a limited degree to predict hepatic histology. In a study /49/, patients with a fatty liver index below 20 had normal ALT and the levels of those with a fatty liver index above 60 h were twice as high. The alcoholic liver disease/NAFLD index score, the fibrosis score and the BARD score are significant for NAFLD diagnosis (Tab. 1.2-4 – Modified Child-Turcotte-Pugh score for severity assessment of a liver disease). Diagnostic assays for comorbidities are important (see Tab. 1.2-5 – Biomarkers in hepatopathies).

Alcoholic hepatopathies – Generalized /5051/

Alcohol abuse leads to a whole spectrum of hepatopathies that may range from metabolic steatosis to fatty liver with toxic degenerative cell damage to alcoholic hepatitis to liver cirrhosis and finally to hepatocellular carcinoma.

– Alcoholic fatty liver

The alcoholic fatty liver is inapparent or non-characteristic in most cases. The GGT is elevated in 80% of the cases, the ALT shows borderline levels or is mildly elevated, the De-Ritis ratio is usually above 2. More severe steatosis is characterized by more pronounced enzyme elevations, especially the GGT is 2-fold elevated, the CHE activity is near the upper reference limit and the mean corpuscular volume of erythrocytes is elevated.

– Fatty liver with toxic pan acinar steatosis

Cholestasis can develop in cases of severe hepatomegaly with toxic pan acinar steatosis. Aminotransferases are mildly to moderately elevated, whereas the GGT and ALP levels are elevated more pronouncedly. In cases of toxic alcohol damage with microvascular steatosis where patients show severe disorders, aminotransferases are elevated pronouncedly, and the De-Ritis ratio is 3–5 because the AST is elevated about 10-fold and the ALT about 2–3-fold.

– Alcoholic hepatitis

The clinical spectrum of alcoholic hepatitis ranges from asymptomatic to chronic, persistent and chronic progressing courses to fulminant alcoholic hepatitis. The aminotransferase and GGT levels in asymptomatic alcoholic hepatitis are similar to those in fatty liver. In the chronic persistent course, aminotransferases are up to 2-fold elevated, the De-Ritis ratio is below 1 and GGT is 3–5-fold elevated. The chronic progressive form is characterized by 2–6-fold elevated AST, up to 4-fold elevated ALT, a De-Ritis ratio above 2 and 10–15-fold elevated GGT. Acute alcoholic hepatitis is a disorder associated with acute abdomen and leukocytosis, which, although rare, is the more common form of alcoholic hepatitis in women. The liver parenchyma undergoes toxic damage due to acute alcohol exposure. The AST and ALT can be elevated more than 20-fold with a De-Ritis ratio above 1 as a result. The GGT is elevated approximately by the same factor as the aminotransferases, the ALP shows elevations several times the upper reference limit, and hyperbilirubinemia of 10 mg/dL (170 µmol/L) is possible.

Liver cirrhosis /5253/

The chronic inflammatory damage of the liver parenchyma can lead to the development of liver cirrhosis. The development of liver cirrhosis is characterized by the necrotization of liver parenchyma with consecutive parenchyma regeneration and formation of new connective tissue. This results in knotty or pseudo-lobular transformation of the liver parenchyma with septal fibrosis. The spectrum of clinical symptoms ranges from the absence of symptoms to life-threatening complications such as portal hypertension with varication and ascites, spontaneous peritonitis, hepatic encephalopathy and carcinoma starting from the hepatocytes or bile duct epithelia. The incidence of new cases in the USA and Europe is reported to be 250 per 100,000 inhabitants per year. Liver cirrhosis can be caused by a variety of previous medical conditions. In Europe and the USA, the focus is on alcohol-toxic etiology, followed by hepatotropic viral, cryptogenic and primary biliary liver cirrhosis. Other etiologies include, for example, autoimmune disorder and Wilson’s disease, α1-antitrypsin deficiency, hemochromatosis, drugs, xenobiotics, chronic cholestatic liver diseases, glycogenosis type IV, galactosemia, tyrosinemia.

Laboratory findings: aminotransferases in viral, cryptogenic, alcohol-toxic and primary biliary cirrhosis are 2–5-fold higher than the upper reference limit on average. The enzyme activity declines with increasing cellular necrosis and is only just above or even within the reference interval; in contrast, the De-Ritis ratio increases. The ALP, GGT and immunoglobulins can be helpful for etiological classification. In alcohol-toxic cirrhosis, the GGT is 5–10-fold the upper reference limit and IgA is elevated compared to IgG and IgM. In serum protein electrophoresis, the increase in IgA causes a fusion of the β and γ-globulin fractions. Primary biliary cirrhosis shows a 2–5-fold elevation of ALP and GGT, a pronounced increase in IgM compared to the other Ig classes and the presence of anti-mitochondrial antibodies. The decline in CHE and albumin and the extension of the prothrombin time are a measure of the reduction in functional liver mass.

Hepatocellular carcinoma /54/

Primary hepatocellular carcinoma is the fifth most common cancer and the third most common cause of cancer mortality worldwide. About 560,000 cases of this type of carcinoma are diagnosed and 550,000 patients die of it every year. 75–90% of liver carcinomas are hepatocellular carcinomas (HCC). The majority of liver cancer cases occur in the sub-Saharan region in Africa and in East Asia and China. In these regions (except Japan), HCC is caused by HBV infection in combination with liver cirrhosis (80%). The prevalence of HCC in regions with a lower risk, such as northern Europe and North America is 1.5 to 4 per 100,000 inhabitants. Liver cirrhosis due to HCV infection or excessive alcohol consumption are the main causes.

Laboratory findings: the liver enzymes do not show a typical behavior in HCC. However, the prevalence of HCC is about 3-fold higher in patients with HCV-associated liver cirrhosis if the ALT is higher than 80 U/L for 3 years /55/. Elevated LD and GGT at relatively unchanged ALP can also be indicative of the disease. It is recommended to use α-fetoprotein (AFP) as a tumor marker of HCC. However, AFP is not suited for screening. A concentration of 20 µg/L represents the optimal balance between diagnostic sensitivity and specificity, but diagnostic sensitivity is only 60%. Given a cut-off value of 200 µg/L, sensitivity is only 21%. According to the criteria of the 2,000 EASL Conference, the diagnosis of HCC is confirmed if an arterial hyper vascular lesion of more than 2 cm diameter is detected by two imaging techniques or such a lesion is detected by one imaging technique at an AFP concentration higher than 400 µg/L.

Cholestatic syndromes – Generalized /56/

Cholestasis is anatomically subdivided into extrahepatic and intrahepatic forms, and intrahepatic cholestasis is further subdivided into obstructive and non-obstructive forms. Extrahepatic cholestasis is caused, for example, by the obstruction of the bile duct by a biliary calculus, carcinoma of the head of pancreas or occlusion of the minor duodenal papilla. Intrahepatic cholestasis in adults can be caused by: disturbances in bile formation by the hepatocyte (hepatocellular cholestasis), a reduction in bile secretion by the cholangiocytes lining the bile ducts (ductular cholestasis), intrahepatic obstruction (HCC, metastases, granulomas, amyloidosis, sarcoidosis). Hepatocellular and ductular cholestasis can result from molecular changes in the transport systems due to the missing expression of transport proteins, disturbance of the transport systems, for example, by enterotoxins (sepsis), drugs (oral contraceptives, metamizole, cyclosporin A, chlorpromazine, erythromycin, amoxicillin, clavulanic acid), pregnancy, hepatitis (viral hepatitis, alcoholic hepatitis) or total parenteral nutrition.

Laboratory findings: the screening pattern of ALT, ALP, GGT and CHE provides information to decide whether cholestasis is the leading symptom of the liver disease. Pronounced elevation of the ALP or GGT compared to ALT is an indication. The extent of CHE reduction indicates an advanced stage and/or the severity of the cholestatic liver disease. By contrast, concomitant cholestasis is present if the ALT is more strongly elevated than the GGT.

– Extrahepatic obstructive jaundice

In acute obstruction by a calculus after biliary colic, the ALT reaches a peak value of up to 10-fold the upper reference limit after 24 hours and then decreases again. GGT and ALP are elevated, with peak levels of about 10-fold (GGT) and 5-fold (ALP) the upper reference limit reached around day 4 of the disease. The bilirubin concentration rises above 15 mg/dL (257 µmol/L). Bile duct obstruction by a tumor is characterized by a slowly progressing increase in bilirubin at normal to mildly elevated ALT /57/.

– Acute hepatitis, cholestatic course

The cholestatic form can occur in viral, alcoholic and drug-induced hepatitis. The cholestatic form of acute hepatitis occurs in 1–2% of the cases of acute hepatitis A and less often in acute hepatitis B, but in 58% of the cases of acute hepatitis E. Compared to the typical icteric course, the cholestatic forms of the disease show a more pronounced increase in GGT and ALP in relation to the aminotransferases and about twice as high a bilirubin concentration of approximately 20 mg/dL (342 µmol/L). Cholestasis can be present in up to two thirds of the cases of fulminant alcoholic hepatitis. Drug-induced cholestasis manifests clinically with symptoms such as fever, arthralgia, myalgia and general malaise 1–6 weeks after drug intake. The ALT is 5-fold elevated at the maximum, the ALP is 2–3-fold elevated, and eosinophilia occurs in 20–50% of the cases. The levels return to normal within 4 weeks after the drug has been discontinued /58/.

– Bacterial infections

Bacterial infections of organ systems or sepsis can lead to cholestasis without hepatic infection. This can be the case, for example, in neonates and infants in the course of urogenital infection with E. coli, and in adults in the course of sepsis or in intra-abdominal complications due to gram-negative bacteria after abdominal surgery /58/. About 2–5-fold elevation of ALT, ALP and GGT and a surge in bilirubin to peak concentrations of 5–10 mg/dL (85–171 µmol/L) can occur.

– Idiopathic postoperative cholestasis

Ischemia and/or hypoxia of the liver are the most common causes of this form of cholestasis.. It occurs, for example, 1–2 weeks after coronary bypass surgery, has a benign course and disappears again. The ALT shows normal or borderline levels, GGT and ALP are 2–5-fold elevated, and bilirubin can be elevated to as high as 5 mg/dL (85 µmol/L) /58/.

Parenteral nutrition

Under total parenteral nutrition, about 25% of pre term neonates and two thirds of adults with inflammatory abdominal disease develop cholestasis. The disease manifests 2–3 weeks after the start of parenteral nutrition and stops after parenteral nutrition has been discontinued. ALT, GGT and bilirubin are mildly elevated /58/.

Hypoxic hepatopathy /59/

Hypoxic hepatopathy, also known as shock liver syndrome, is associated with a rapid elevation of aminotransferases to 100-fold the upper reference limit and occurs following cardiogenic shock, severe blood loss, sepsis, postoperative hypotension or pulmonary embolism. GLD is elevated pronouncedly due to hepatocellular necrosis and can reach levels comparable to those of the aminotransferases. In a study /59/, 29 of 56 patients with AST higher than 100-fold the upper reference limit had hypoxic hepatopathy. Mortality was 55% referring to all 56 patients. Chronic heart failure with congestive hepatomegaly caused bilirubin concentrations of up to 20 mg/dL (342 µmol/L), elevated ALP and up to 15-fold elevated aminotransferases.

Fulminant hepatic failure /60/

Fulminant hepatic failure is a severe damage of the liver parenchyma in otherwise healthy individuals with no previous liver disease. Symptoms appear quickly; hepatic encephalopathy occurs in acute liver failure within 2 weeks after the onset of jaundice and in subacute liver failure within a period of 2 weeks to 3 months. Causes are: Infection with hepatotropic viruses, especially fulminant viral hepatitis B, drugs such as acetaminophen (paracetamol), non-steroidal antiphlogistics, sulfonamides, tetracyclines, intoxication with carbon tetrachloride, yellow phosphor, Amanita phalloides, Bacillus cereus toxin, ecstasy, acute pregnancy fatty liver, Budd-Chiari syndrome. Typical complications include encephalopathy with cerebral edema, cardiovascular and respiratory problems, renal insufficiency, coagulopathy and sepsis.

Laboratory findings: aminotransferases are higher than 1,000 U/L, the prothrombin time (PT) is much extended and creatinine is elevated. The following combinations indicate orthotopic liver transplantation:

  • pH below 7.3 in paracetamol intoxication or the following three criteria: PT below 10%, creatinine above 3.5 mg/dL (309 µmol/L), encephalopathy grade III.
  • In other causes: PT below 20%, bilirubin above 17.5 mg/dL (300 µmol/L), under 10 or over 40 years of age, over 7 days of jaundice before the onset of encephalopathy.

Hepatopathies in pregnancy – Generalized /61/

During pregnancy, ALT, AST and GGT remain within the reference interval, the ALP can be 1.5–4-fold elevated. New liver diseases occur in less than 0.1% of pregnancies. Jaundice and/or elevated ALT require quick differential diagnosis. Aminotransferases can be elevated due to uterine muscle contraction during delivery.

– Hyperemesis gravidarum (HG)

HCG occurs in the first trimester in 1–20 of 1,000 pregnant women. The aminotransferases can be elevated up to 5-fold and the ALP up to 2-fold the upper reference limit and bilirubin can be elevated up to 4 mg/dL (68 µmol/L).

– Preeclampsia, eclampsia

Preeclampsia occurs in the second or third trimester and affects 5–7% of pregnant women. It is characterized by the triad of hypertension, proteinuria and peripheral edema. Spasms and coma are added in eclampsia. Elevated aminotransferases (usually under 10-fold) indicate liver involvement. ALP is also elevated. Symptoms of preeclampsia already show weeks before the clinical signs and include thrombocytopenia and elevated cystatin C. See also Section 38.9.1 – Preeclampsia.

– HELLP syndrome

The hemolysis (H), elevated liver enzyme (EL) and low platelet count (LP) syndrome affects 0.1–0.6% of pregnancies and occurs before delivery in 70% and after delivery in 30% of the cases. The complement and coagulation cascades are activated, as in preeclampsia. This results in generalized endothelial and microvascular damage that leads to microvascular angiopathic hemolytic anemia.

Laboratory findings: aminotransferases are elevated up to 80-fold, haptoglobin is low and Burr cells and schistocytes are found in the blood smear, thrombocytopenia up to 6 × 109/L.

– Fatty liver

Acute fatty liver of pregnancy (AFLP) occurs in the last trimester of pregnancy. The incidence is 1 in 10,000–15,000 pregnancies. Maternal mortality is 18%. The enzyme long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) is defective. The deficiency is based on mutations G1528C in 60% of cases and E474Q in 19% in the LCHAD gene. LCHAD deficiency leads to an accumulation of long-chain fatty acids in the liver. Symptoms include nausea, vomiting, abdominal pain, anorexia.

Laboratory findings: hyperbilirubinemia, leukocytosis and hypoglycemia are diagnostic prodromes of AFLP. In the clinical phase, the aminotransferases are elevated up to 10-fold and the bilirubin concentration can increase up to 10 mg/dL (171 µmol/L). The differentiation of AFLP from the HELLP syndrome is based on hypoglycemia, PT extension and aPTT.

– Intrahepatic cholestasis

Intrahepatic cholestasis of pregnancy (ICP) does not occur before week 26 of pregnancy. The incidence is 1 in 1,000–10,000 pregnancies and affects pregnant women of older age, multiparas and occurs with familial accumulation. Women with cholestasis under oral contraceptives and the HLA characteristics B8 and B16 are affected more frequently. Pruritus is a common symptom and starts 1–4 weeks before the onset of jaundice.

Laboratory findings: the aminotransferases are 2–10-fold elevated and the ALP can be normal or elevated up to 4-fold. Bilirubin rarely exceeds 5 mg/dL (85 µmol/L), the direct form is elevated. The bile acid concentrations in serum are always elevated (10–25-fold).

Unspecific co-reaction of the liver

An unspecific co-reaction of the liver can occur, for example, in rheumatic diseases, pulmonary and renal diseases, upper abdominal diseases, pancreatitis, anesthesia and sepsis. Only one in three ALT elevations is based on primary liver disease, the elevated levels are much more often due to an unspecific co-reaction of the liver.

Drug-induced hepatotoxicity – Generalized /6263/

Adverse drug events in the liver occur in up to 1% of drug-exposed patients and in up to 4% of patients exposed to amiodarone, isoniazid and valproic acid. Acute liver failure is caused by drugs in 55% of the cases, where prescription drugs and herbal medicinal products are responsible for 22.5% and the non-prescription drug paracetamol is responsible for 77.5%. Drugs can induce various forms of liver diseases. Laboratory findings allow a rough distinction between hepatitic, cholestatic and combined cholestatic/hepatitic types of injury based on the ALT and ALP activities. The clinical course of the latter type corresponds to that of cholestatic injury. A structured causality assessment is presented in Ref. /62/.

Laboratory findings: elevated ALT without elevated ALP indicate hepatitic injury (ALT elevated more than 2-fold and/or ALT/ALP elevation ratio above 5). Elevated ALP without elevated ALT (ALP elevated more than 2-fold and/or ALP/ALT elevation ratio above 5) is indicative of a cholestatic type. Elevated levels of both enzymes (ALT elevated more than 2-fold, combined with elevated ALP and an ALT/ALP elevation ratio of 2–5) are indicative of a combined cholestatic/hepatitic type. A correlation between elevated enzyme levels due to liver injury and drug intake is to be assumed if the elevation occurs 5–90 days after drug intake. A decrease in enzyme activity supports the causal relationship of drug-induced liver injury because most injuries are reversible after intake of the drug is discontinued.

– Paracetamol /64/, INH, troglitazone, halothane, sulfonamides

These drugs have a dose-dependent hepatotoxic effect and can cause fulminant hepatic failure. Hepatotoxicity from paracetamol in adults is rare with doses less than 150 mg/kg body weight. The potentially toxic dose varies significantly because the metabolization of paracetamol can fluctuate by a factor of 60 in different individuals. In adults, the long-term intake of 6 g per day can cause hepatocellular injury; alcohol and enzyme inductors such as phenytoin and rifampicin increase the hepatotoxicity of paracetamol. If fulminant hepatic failure is suspected, it is prognostically valuable to determine the plasma half-life of paracetamol (see also Section 48.1 – Indication). No severe complications are to be expected with aminotransferase levels of up to 1000 U/L.

– NSAID /63/

Non-steroidal anti-inflammatory drugs (NSAID) are among the most common prescription drugs. The incidence of NSAID-induced liver injury is estimated to be 5 per 100,000 individuals.

Cyclooxygenase 2 (COX-2) inhibitors: depending on their COX-2/COX-1 selectivity, the inhibitors are classified into selective (celecoxib, refocoxib), preferential (nimesulide, meloxicam) and non-selective (aspirin, diclofenac, ibuprofen, indometacin) COX inhibitors.

  • Selective (COX-2) inhibitors: These inhibitors can cause hepatitic or cholestatic/hepatitic injury. Elevated enzyme levels occur 4 days to 4 weeks after treatment is started. Discontinued treatment results in declining enzyme levels after 1–4 weeks. Some of the patients develop eosinophilia.
  • Preferential (COX-2) inhibitors: Nimesulide can cause hepatitic injury with increasing ALT levels 1–15 weeks after treatment is started. Normal ALT is restored 2–17 months after treatment is discontinued. Acute hepatitis (meloxicam) and fulminant hepatic failure (etodolac) have also been described.
  • Non-selective (COX-2) inhibitors: Ibuprofen very rarely causes liver injury. Sulindac causes liver injury of the cholestatic type (43%), hepatitic type (25%) and an indefinable type. 66% of symptomatic patients show a hypersensitivity reaction (eosinophilia, fever, rash). Diclofenac causes liver injury in 1–5 per 100,000 individuals. The liver injury manifests as acute hepatitis, cholestatic hepatitis or chronic hepatitis. The enzymes return to normal after the intake of diclofenac is discontinued, and the prognosis is good.

Newer anti-inflammatory drugs: leflunomide has an immunomodulatoy effect and is used to treat rheumatoid arthritis. The ALT is found to be elevated 2-fold in 6.6% and 3-fold in 4.4% of the cases. It is recommended to determine the ALT prior to drug intake and perform monitoring monthly in the first 6 months and every other month thereafter. Moreover, it is recommended to reduce the dose if the ALT is 2-fold the upper reference limit and discontinue treatment if the ALT is 3-fold the upper reference limit. Only a small number of cases of liver injury have been described for infliximab, a monoclonal antibody against tumor necrosis factor used in Crohn’s disease. Treatment with zafirlukast, a leukotriene receptor antagonist prescribed in cases of mild asthmatic symptoms, induces elevated ALT levels higher than 2-fold the upper reference limit within 3 months in 3.3% of the patients and after 5–13 months in other patients.

– Antihypertensives /63/

α-methyldopa is hardly prescribed anymore; however, it is known to induce elevated aminotransferases in 10–30% of the cases and liver injury manifested as acute hepatitis (below 1%). Elevated ALT levels occur within the first 3 months in 5% of the patients. As a rule, the patients are asymptomatic, over 50 years of age and have taken α-methyldopa for 1–4 weeks. Beta-adrenergic receptor blockers (propranolol, metoprolol, acebutalol) only have low hepatotoxic potential (except labetalol). Calcium channel antagonists such as diltiazem can induce acute hepatitic liver injury, cholestasis and granulomatous liver injury. Angiotensin-converting enzyme (ACE) inhibitors (captopril, enalapril, fosinopril) can induce bland cholestasis or cholestatic hepatitis. Elevated enzyme levels occur 1 week to 1 year after treatment is started. A hypersensitivity reaction with fever, rash and eosinophilia can also occur. Angiotensin-II receptor antagonists (irbesartan, candesartan, losartan) can cause cholestatic hepatitis.

– Oral antidiabetic drugs /63/

Sulfonylureas (chlorpropramide, glibenclamide, glyclazide) can cause liver toxic damage associated with a hypersensitivity reaction. Metformin has been described to cause cholestatic hepatitides. Glucosidase inhibitors are prescribed for adjuvant therapy of diabetes mellitus type 2. After 2–8 months of therapy, acarbose in doses higher than 100 mg/day can cause hepatocellular injury. The second generation of thiazolidinediones (rosiglitazone, pioglitazone) causes elevated ALT levels of up to 3-fold the upper reference limit in 0.25% of patients. The elevation occurs 1–3 weeks after start of therapy. According to the FDA, the ALT should be below 2.5-fold the upper reference limit before start of therapy and controlled every 2 months. Therapy is discontinued if the ALT is persistently higher than 3-fold the upper reference limit.

– Lipid-lowering agents /63/

Hypercholesterolemia is an essential risk factor in the development of cardiovascular disease. Lowering of cholesterol by HMG-CoA reductase inhibitors (HMG-CoA, hydroxymethylglutaryl-CoA), the statins (e.g. atorvastatin, lovastatin, pravastatin), can reduce the rate of myocardial infarction and stroke. Therapy leads to elevated ALT in 3% of patients and increase in CK in 20–30% of patients within 3 months. The elevations are reversible after therapy is discontinued and do not require termination of therapy. Severe liver injury develops in 0.2 of 100,000 treated patients. Statins are contraindicated in liver diseases, myopathies and during pregnancy.

– Anti-epileptic drugs /63

The triad of fever, rash and inner organ involvement is a hypersensitivity symptom. It is based on the Reactive Metabolite Syndrome (RMS). RMS is diagnosed within the scope of phenytoin, phenobarbital, carbamazepine or lamotrigine therapy. RMS is seen in 10–100 of 100,000 patients treated with the above-mentioned anti-epileptic drugs. The symptoms start with fever, nausea and rash 1–8 weeks after start of therapy. Lymphadenopathy and leukocytosis can occur systemically, the levels of ALT and other liver enzymes are elevated in 50% of the cases, and severe hepatitis occurs occasionally. Valproic acid therapy causes liver injury in 1 of 37,000 treated patients. However, the incidence in children under 3 years of age and with certain diseases (urea cycle disorder, fatty acid oxidation disorder) is 1: 500. Lamotrigine can cause acute hepatitis in individual cases 2–3 weeks after start of therapy. The incidence of hepatotoxic cases is 3–4/100,000 for felbamate and lower for topiramate. Valproic acid very rarely causes the Stevens-Johnson syndrome, a bullous form of erythema multiforme. It can be associated with severe liver injury and aminotransferase levels as high as 6,000 U/L /65/.

– Psychotropic drugs /63/

Anti-psychotic and sedative-hypnotic drugs: Chlorpromazine, haloperidol, pro chlorpromazine and sulpiride can cause cholestatic liver injury, whereas clozapine and risperidone cause hepatocellular injury. Benzodiazepines do not result in liver injury, except for clotiazepam that can cause severe hepatitis and bentazepam that can cause chronic hepatitis.

Antidepressants: the selective serotonin reuptake inhibitors (fluoxetine, paroxetine, sertaline) are the main antidepressants prescribed. Up to 0.5% of patients develop hepatocellular injury with elevated ALT after several weeks to 1 year. Acute hepatic failure (nefazodone) and acute and chronic hepatocellular injury (trazodone) have been described for other antidepressants.

– Cyclophosphamide, busulfan, azathioprine

Acute hepatic vein occlusion can occur under cytostatic therapy with alkylating reagents. The focus is on hepatocellular injury with elevated aminotransferase levels.

– Oral ovulation inhibitors, danazol

Sex hormones, especially C17-alkylated testosterone, cause reduced bile flow through Na+-K+-ATPase inhibition which results in canalicular cholestasis. During the first or second cycle, GGT and ALP are elevated, and the aminotransferases vary and do not exceed 5-fold the upper reference limit. Bilirubin can exceed 10 mg/dL (171 µmol/L). Liver tumors in the form of adenomas, focal nodular hyperplasia and hepatocellular carcinoma after years of intake of hormonal contraceptives still containing rather high hormone doses have been described. The occurrence of hepatocellular carcinomas after danazol therapy has also been reported. Liver enzymes are normal and do not become elevated until the necrotizing process starts.

– Heparin

According to a study /66/, subcutaneous treatment with 5000–15,000 IU of unfractionated heparin within 8 hours leads to elevated ALT in 89%, elevated AST in 82% and elevated GGT in 37% after one hour. Peak levels are reached around day 8 of treatment, with ALT elevated 3-fold and AST elevated 2-fold the upper reference limit on average. Activities return to the initial levels if heparin treatment is continued.

– Methotrexate /67/

In treatment of rheumatic patients with one dose a week and on condition that there is no alcohol abuse, the incidence of toxic liver injury is 1 in 1,000 cases based on 5 years of treatment. The American College of Rheumatology recommends that ALT and AST be determined every 4–8 weeks. If more than half of the results are pathological within a year, methotrexate treatment should be stopped. Moreover, treatment should be modified if the serum albumin concentration is below 3.5 g/dL during monitoring.

– Amiodarone

Hepatopathy is one of the adverse events of the anti-arrhythmic agent amiodarone besides corneal and pulmonary changes, light sensitization and dysfunction of the thyroid gland (see Tab. 30.3-1 – Reference intervals for TT4 and FT4). Fatty acid oxidation dysfunction under amiodarone therapy leads to hepatocellular steatosis.

– AIDS therapy

Some of the HIV patients under antiretroviral therapy without hepatitis B and hepatitis C infection have elevated aminotransferases. In a study /68/, the majority of HIV infected patients with ALT levels above 80 U/L had non-alcoholic steatohepatitis.

– Ecstasy /69/

Ecstasy, the popular street name for N-methyl-3,4-methylendioxy-amphetamine or 3,4 methylendioxy-methamphetamin (MDMA), induces hepatic, cardiovascular and cerebral toxicity and has hyperpyretic effects. Liver injury is hepatitic and similar to viral hepatitis. Patients experience increased bleeding tendency.

– Xenobiotics (see Tab. 1.9-4 – GGT in hepatic and biliary tract diseases), e.g. carbon tetrachloride, mushroom poisons (phalloidin, phalloin)

Consequences of toxic liver injury due to environmental toxins can range from enzyme induction, fatty liver, hepatitis, fibrosis and cirrhosis to tumor development. Jaundice is rare and indicates a severe disorder. The toxic effect of carbon tetrachlorides and mushroom poisons on liver cells, for example, is directly dose-dependent. Carbon tetrachloride intoxication causes massive hepatocellular zone 3 necrosis with immediately elevated aminotransferases. In contrast, in death cap poisoning, elevated enzyme levels do usually not occur before the 3rd day after the mushroom meal (two-phase course of the intoxication: latency period of about 12 hours followed by nausea, vomiting, diarrhea; onset of the hepatitic phase on the third day). The aminotransferase and bilirubin levels are only loosely correlated with the severity of intoxication. The prothrombin time is an important prognostic indicator. In a study /70/, 84% of the patients with values below 10% died, but no deaths occurred in patients with values above 40%.

– Herbal medicinal products

Self-medication with herbal medicinal products has increased significantly in recent years. The liver is the essential organ for the biotransformation of these products and is therefore preferentially damaged. For detailed information, see Ref. /71/.

Autoimmune disorders of the liver and bile ducts

Autoimmune disorders of the liver include autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). These disorders are characterized by disturbed immune tolerance toward liver tissue (i.e., toward hepatocytes in AIH and toward bile duct cells in PBC and PSC) and classified as chronic inflammatory diseases. Association with specific HLA types indicates a genetic predisposition. Moreover, there is an association with extrahepatic autoimmune disorders /72/.

– Autoimmune hepatitis (AIH)

AIH is a chronic progressive hepatitis of unknown cause that affects children and adults at any age. Occasionally, it takes a fluctuating course with episodes of elevated or low activity. It is important to distinguish AIH from other forms of chronic hepatitis because a large proportion of patients respond to anti-inflammatory or immunosuppressive therapy or a combination of the two /73/.

Laboratory findings: the elevation of the aminotransferases corresponds to the extent of hepatocellular injury and shows no correlation with inflammatory activity. Thus, 2–50-fold elevations have been measured. The ALP is only mildly elevated (ALP/ALT ratio of elevation below 1.5). IgG elevation is diagnostically significant; IgG concentration can be 1.1–3-fold the upper reference limit. Autoantibodies against ANA, smooth muscles, actin, SLA/LP, pANCA, LKM-1 and LC-1 are detected. HLA typification shows an association with HLA-DR3 or HLA-DR4. Criteria for AIH diagnosis are listed in Section 25.8.3 and under Ref. /74/.

– Primary sclerosing cholangitis (PSC)

PSC is a chronic cholestatic liver disease of unknown origin. It is characterized by progressive inflammation with destruction and fibrotization of the intrahepatic and extrahepatic bile ducts. In the USA and Europe, a considerable proportion of inflammatory bowel diseases is associated with PSC. The prevalence is 1–4 per 100,000 inhabitants, approximately 70% of affected individuals are men. The mean age is 40 years. Symptoms occur 12–24 months before clinical diagnosis. Gradually increasing fatigue and pruritus followed by jaundice are the most common symptoms; other clinical symptoms include hepatomegaly, splenomegaly, hyperpigmentation, xanthelasmas and xanthomas. PSC is one of the most common chronic cholestatic diseases in adults and one of the most common indications for orthotopic liver transplantation in the USA.

Laboratory findings: at the time of diagnosis, ALT is only mildly elevated and GGT and ALP are about 5-fold elevated; up to two thirds of the patients have hyperbilirubinemia. Cerulopasmin and copper in serum are also elevated, and copper excretion in urine is increased. Hypergammaglobulinemia is found in 30% and elevated IgM is found in 30–50% of the patients. About 65% of the patients with PSC have antibodies against perinuclear anti-neutrophil cytoplasmic antigens (pANCA) and show an association with HLA-DRw52a /7375/.

– Primary biliary cirrhosis (PBC)

PBC is a chronic progressive disease causing the destruction of small and medium bile ducts. Histologically, a granulomatous inflammatory transformation of the interlobular and septal bile ducts takes place. The prevalence of PBC is 4–6 per 100,000 inhabitants. It affects women 6–10 times more frequently than men at 40–60 years of age. Asymptomatic patients have been increasingly diagnosed with the disease since the determination of ALP, IgM and anti-mitochondrial antibodies (AMA) was introduced in patients with hepatomegaly or suspected autoimmune disorder. The clinical focus is on symptoms such as pruritus, fatigue or upper abdominal pain.

Laboratory findings: at the time of diagnosis, one to two thirds of the patients have hyperbilirubinemia, almost all patients have elevated ALP, elevated IgM and a pathological AMA titer /76/. The ALT is usually within the reference interval. Association with the haplotype HLA-DRw8 is 6 times more common in these patients than in normal individuals.

Liver metastases

The changes in enzyme levels to be expected depend on the location, size and number of metastases. According to a study /77/, the incidence of increase in enzyme levels was as follows: GGT 88%, ALP 79%, AST 64%, LD 63%, ALT 55%, GLD 52%, bilirubin 40%. CHE was decreased in 59% and the prothrombin time in 29% of the cases; the De-Ritis ratio was above 2.

Anorexia nervosa /78/

About 30% of patients near the nadir of body weight due to longer-term immoderate food restriction can have median ALT levels of up to 10-fold and median AST levels of up to 8-fold the upper reference limit. The aminotransferases are positively correlated with the body mass index. Under dietetic treatment, one third of the patients with no previous elevations show elevated aminotransferases. Peak levels are reached after about 20 days; the median ALT is about 2-fold higher and the median AST is about 1.5-fold higher than the upper reference limit.

Heat stroke

Heat stroke causes elevated enzyme levels. Patients show 2–6-fold elevated LD, up to 50-fold elevated CK, about 3-fold elevated ALT and up to 20-fold elevated AST in the first 24 hours after hospitalization. The AST and LD levels are considered prognostic indicators. Patients with AST higher than 1000 U/L are to be considered seriously ill and have a poor prognosis /79/.

α1-antitrypsin deficiency

See Tab. 18.5-3 – AAT deficiency.

Wilson’s disease

Children with Wilson’s disease have elevated ALT of about 5-fold the upper reference limit on average in 95% of the cases. Under penicillamine or zinc treatment, the levels decrease to the reference interval after 17 months (median) in 80% of the patients. The ALT persist at about 2-fold the upper reference limit in the other patients /80/. See also Tab. 18.7-3 – Wilson disease.

Table 1.6-4 Aminotransferases in cardiac disease

Clinical and laboratory findings

Myocardial infarction

AST can be used for monitoring myocardial infarction; ALT can be used if liver involvement is suspected. Elevated AST levels occur from 6–12 hours after the acute event, reach a peak of up to 5-fold the upper reference limit on average within 16–48 hours and become normal again on day 3 to 6. Elevations of ALT are inconsistent and mild; the De Ritis quotient is more than 2. Elevated AST is measured in more than 95% of patients with precisely localizable infarction within the first 24 hours. If the infarction cannot be localized or is not transmural, the incidence of AST elevation is significantly lower. The AST activity depends on the size of the infarction; the mortality rate is significant in patients with levels more than 10-fold the upper reference limit /81/. Very high AST levels occur in cardiogenic shock.

Pulmonary embolism

Clinical differentiation between pulmonary embolism and myocardial infarction is not always easy. According to laboratory test results, there are mild elevations in aminotransferase and LD levels in approximately 20% of the cases; CK is mostly normal.

Myocarditis

CK and AST can be elevated mildly. Accelerated erythrocyte sedimentation rate as well as slight to moderate leukocytosis in approximately 50% of the cases /82/.

Pericarditis

AST can only be elevated if myocarditis is present in addition.

Cardiac irregularity

Supraventricular or ventricular tachyarrhythmias can cause mild AST elevations if the ventricular rate exceeds 180/min.; this also applies to electrical cardioversion.

Cardiac catheterization

Mild elevations of AST, CK and LD have been described.

Pacemaker implantation

No elevated AST and CK levels have been measured.

Open-heart surgery

Elevated AST, CK and LD activities have been recorded within the first hours after surgery /83/.

Table 1.6-5 Aminotransferases in skeletal muscle damage (see also Tab. 1.8-5 – Chronic skeletal muscle damage (general)/84/

Clinical and laboratory findings

Progressive muscular dystrophy

All types of the disease (type I, facioscapulohumeral type; type II, limb/girdle type; type III, Duchenne type) are associated with elevated aminotransferases; the De Ritis quotient is more than 1. AST is elevated up to approximately 50-fold the upper reference limit in types I and II and up to 100-fold the upper reference limit in type III. AST is already elevated before the disease starts and reaches peak levels at the onset of clinical symptoms.

Lower AST levels during the course of the disease indicate slower progression and a more favorable life expectancy. AST and CK levels decline over the years and reach the reference interval in the final stage.

Myositis

The acute and subacute forms of polymyositis cause significant elevations of AST, whereas levels are normal or mildly elevated in the chronic form of the disease. AST can be mildly elevated and ALT is normal in dermatomyositis. Ocular myositis has normal AST activities.

Hypothyroid myopathy

Mild elevations of AST, CK and LD are measured in prolonged hypothyroidism.

Epileptic state

Elevations of CK, LD, AST and ALT occur. The activity course in the epileptic state corresponds to that during myocardial infarction; however, elevations are more pronounced and the ALT is elevated. Enzyme levels are lower in grand mal seizure than in the epileptic state; however, they are higher in alcohol-induced seizure than in an idiopathic seizure. After a grand mal seizure, the CK behaves similarly to that after myocardial infarction; the other enzymes show no correlated behavior, but the ALT is also elevated in many cases. Prolactin is also elevated significantly.

Malignant hyperthermia

This condition occurs in approximately 1 of 20,000 narcoses and is lethal in 60% of the cases. Symptom-free patients experience high fever and muscle rigidity following administration of halothane, muscle relaxants, etc. Aminotransferase and CK levels do not rise before 24 hours. Malignant hyperthermia is an autosomal-dominant disorder and occurs more commonly in men /85/.

Physical labor can cause elevated AST of various degrees and, more rarely, elevated ALT, depending on intensity, duration and fitness level. A 2–3-fold elevation of AST and mildly elevated ALT have been described in marathoners. Anabolic drugs and physical exercise (bodybuilders) can cause elevations of AST and ALT to 2-fold the upper reference limit /86/.

Table 1.7-1 Principle of CHE determination (top) and calculation of dibucaine number (bottom)

Butyrylthiocholine + H 2 O ChE thiocholine + butyrate Dibucaine number = (1 – ChE inhibited ) × 100 ChE uninhibited

Table 1.7-2 Chromogenic reactions for measuring the thiocholine produced

1.

thiocholine + 5,5’dithio-bis-2 nitrobenzoate (DTNB) 5-mercaptothiocholine-2-nitrobenzoate + 5 thio-2-nitrobenzoate.

Measured at 405 to 410 nm

2.

thiocholine + 2 OH + 2 [Fe(CN)6]3–

dithiobis(choline) + H2O + 2 [Fe(CN)6]4– (recommended reaction according to Ref. /4/).

Measured at 405 nm.

Table 1.7-3 Cholinesterase reference intervals

Butyrylthiocholine 37 °C /10/

Benzoylcholin 37 °C /11/

3,93–10,8 (65–180)

0,66–1,62 (11–27)

4,62–11,5 (77–192)

0,66–1,62 (11–27)

Data expressed in kU/L (μkatal/L) for adults and children.

Conversion: μkatal/L × 60=U/L.

Table 1.7-4 Liver diseases possibly associated with decreased ChE activity

Clinical and laboratory findings

Acute hepatitis

Uncomplicated viral hepatitides cause no, or only slight, reductions in ChE; lower levels occur in necrotic progression depending on the degree of severity. In acute viral hepatitides, normal ChE is found more often than lowered levels. In hepatitis C, ChE levels are supposed to be higher than those in healthy control subjects /16/.

Chronic hepatitis

There are no differences in ChE levels in persistent and active forms of the disease. ChE is normal in approximately 40% of these patients. ChE is especially significant in monitoring. If the absence of inflammatory response and ALT, AST and GGT have possibly returned to normal as a result, a decrease of ChE near to the lower reference limit can be the only pathological indication of liver injury /12/.

Liver cirrhosis

Liver cirrhosis is the organic disease most commonly associated with decreased ChE. In a study /14/, diagnostic sensitivity and specificity were 88%, each. A positive predictive value of 13% was found for lowered ChE in 1,050 examined individuals with a prevalence of 25 cirrhotics, compared to a predictive value of 99.7% for normal ChE. Hence, ChE is not suited for screening for liver cirrhosis because only one in 8 patients with lowered ChE had liver cirrhosis /14/. In contrast, a normal ChE mostly rules out liver cirrhosis. Despite great individual differences, there is a correlation between a decline in ChE and the progression of cirrhosis for all forms of cirrhosis, especially primary biliary cirrhosis and alcohol-toxic cirrhosis. Only 11% of cirrhotics supposedly have normal ChE.

Acutely impaired hepatic blood flow

ChE decline is less pronounced in acutely impaired hepatic blood flow than in acute intoxication. ChE decreases to a minimum of 50% below the lower reference limit in the first case, and even further in the latter case /12/.

Chronic liver congestion

A slight decline in ChE with or without a discrete elevation of GGT can occur.

Liver tumor, liver metastases

The extension of the neoplastic process in metastatic liver and primary liver tumors results in a decline in ChE. ChE levels lowered by 58% occur in liver metastases /17/.

Liver transplantation

Rapid elevation of ChE within a few days indicates that the transplant started working immediately.

Table 1.7-5 Differential diagnostic significance of combined determination of ChE and albumin

ChE

Albumin, CHE

Liver injury

Differential diagnosis

Low

Low

Present (ALT elevated)

Liver cirrhosis

Chronic active hepatitis

Viral hepatitis (~ 1/3 of cases)

Reference interval

None (ALT normal)

ChE inhibited
e.g.., by pesticides

Low

None (ALT normal)

Leukemia, M. Hodgkin

Carcinoma, postoperative conditions

Gastrointestinal disease

Protein malnutrition

Pancreatitis

Renal insufficiency

Chronic hepatitis C

Elevated

Reference interval

None (ALT normal)

Hyperlipidemia

Diabetes mellitus

Atypical ChE variant Cynthia.

Present (ALT mildly elevated)

Fatty liver e.g., due
to alcohol abuse

Low

None

Severe renal protein loss e.g.,
nephrotic syndrom

Normal

Normal

ALT normal

Liver cirrhosis largely excluded predictive value above 99%.

Table 1.7-6 Other diseases possibly associated with reduced ChE activity

Clinical and laboratory findings

Severe disorders, shock, intensive care patients

Severe disorders with a catabolic metabolic state are the most common causes of low ChE levels (e.g., leukoses, post-surgical conditions, severe infectious diseases, malignant diseases of the lymphoreticular system, carcinomas with and without liver metastases) /14/.

Septic shock

According to a study /18/, there is a significant correlation between the level of ChE activity in monitoring and survival. There were more deaths in patients with hepatic dysfunction and ChE activity lowered to 1,484 (512–3,556) U/L on average; the surviving patients had a mean activity of 2,906 (852–9,644) U/L; substrate: butyrylthiocholine.

Chronic inflammatory bowel disease

ChE levels measured in cases of florid Crohn’s disease and florid ulcerative colitis correspond to approximately 60% of those of the healthy collective. Normal levels are reached in remission and partial remission. ChE has been proven to be a good marker for the assessment of disease activity. From an etiological perspective, the inhibition of ChE synthesis within the scope of an acute phase response, most likely induced by endotoxins, is under discussion /19/.

Myopathy

Significantly reduced ChE levels can occur in progressive muscular dystrophy and Thomsen’s disease /20/.

ChE plays no role in the diagnosis of these diseases in comparison with other biomarkers. If reduced ChE activity occurs, it is only short-lived and very discrete. Reduced ChE levels in trichinosis are still traceable up to 6 months after infestation.

Table 1.7-7 Drug-induced inhibition of cholinesterase /21/

Inhibition below 15%:

  • Non-depolarizing muscle relaxants (e.g.; pancuronium, vecuronium)
  • Antibiotics: penicillins, streptomycin

Inhibition 20–100%:

  • Carbamate esters used as parasympathicomimetics, e.g. neostigmine, edrophonium, pyridostigmine, physostigmine
  • Organic phosphoric acid esters applied as pesticides in the form of organophosphates
  • Cardiovascular drugs e.g., quinidine, esmolol
  • Cytostatics, e.g. cyclophosphamide; lowering already occurs on the first day of treatment, normal values are reached within a week
  • Hormones e.g., corticosteroids
  • Hormonal contraceptives
  • Psychotropic drugs e.g., lithium, phenelzine
  • Bronchodilators e.g., bambuterol
  • Glaucoma treatment e.g., ecothiopate
  • Muscle relaxants e.g., succinylcholine

Table 1.7-8 Biochemical characteristics of cholinesterase variants

Geno-
type

Incidence

ChE
(U/L)

Dibucaine
number

Fluoride
number

RoN
number

SC
sensitivity

E1uE1u

95%

660–1,620

79–86

56–65

80–100

none

E1uE1a

1 : 30

373–1,191

56–72

41–53

65–81

rare*

E1uE1f

1 : 200

410–1,255

73–80

41–54

79–100

rare*

E1uE1s

1 : 220

326–900

79–86

56–67

94–100

rare*

E1aE1f

1 : 19,000

320–661

38–55

22–34

56–69

mild

E1fE1f

1 : 160,000

low

60–70

30–42

92–98

mild

E1fE1s

1:170,000

351–509

62–66

16–38

86

mild

E1aE1a

1 : 2,500

169–709

13–28

15–28

19–27

severe

E1aE1s

1 : 20,000

134–469

11–28

16–29

12–25

severe

E1sE1s

1 : 100,000

0–48

severe

E1aE1k

1 : 250

341–826

46–59

34–48

52–64

mild**

E1uE1k

rare*

387–938

79–86

58–66

86–100

rare*

E1uE1h

rare*

370–706

80–86

59–64

96–100

rare*

E1aE1h

rare*

149–246

23–36

22–32

28–32

severe

Data from Ref. /10/, except for incidence and values for genotype E1fE1f, both adopted from Ref. /1/. ChE activity measured with the benzoylcholine method. SC, succinylcholine; * possible during pregnancy, ** in approx. 25% of cases.

Table 1.7-9 Diseases possibly associated with elevated ChE activity /24/

Assessment

Diabetes mellitus

The most common cause of elevated ChE.

Cardiovascular disease

The second most common cause of elevated ChE.

Hyperlipoproteinemia type IV

36% in patients with this type of hyperlipoproteinemia have elevated ChE levels.

Fatty liver

Elevated ChE is often accompanied by elevated ALT and/or AST and/or GGT. In fatty infiltration of the liver as manifestation of secondary liver involvement, elevated ALT can be accompanied by mildly elevated ChE, GLD and GGT levels.

Nephrotic syndrome, exsudative enteropathy

ChE synthesis and albumin synthesis in the liver are coupled with each other. Both diseases result in the loss of albumin and – consequently – compensatorily increased albumin and ChE synthesis.

Hyperthyreosis, severe obesity

Mildly elevated ChE occur in some cases. They are not significant for the diagnosis of these diseases.

Icterus juvenilis intermittens Gilbert-Meulengracht

Mild to moderate ChE elevation can be present.

Cynthiana variant

A familial ChE variant is present where serum activity is increased 2- to 3-fold. There is significant resistance to succinylcholine.

Table 1.8-1 Principle of CK determination

Creatinphosphate + Mg-ADP CK Creatine + Mg-ATP Glucose + ATP HK Glucose-6-phosphate + ADP Glucose-6-phosphate + NADP G-6-PD Gluconate-6-phosphate + NADPH 2

Table 1.8-2 Reference intervals for CK

CK

Adults

  • Outpatients

≤ 170 (2.85)

≤ 190 (3.20) /4/

  • Inpatients

≤ 145 (2.41)

≤ 171 (2.85) /5/

  • Africans

≤ 330 (6.50)

≤ 520 (8.67) /6/

Children /7/

  • 15–18 yrs.

34–147 (0.57–2.45)

28–142 (0.47–2.37)

  • 0–90 days

29–303 (0.48–5.05)

43–474 (0.72–7.90)

  • 3–12 mos.

25–172 (0.42–2.87)

27–242 (0.45–4.03)

  • 3–24 mos.

28–162 (0.47–2.70)

25–177 (0.42–2.95)

  • 2–10 yrs.

31–152 (0.52–2.53)

25–177 (0.42–2.95)

  • 1–14 yrs.

31–152 (0.52–2.53)

31–172 (0.52–2.87)

Data expressed in U/L (μkatal/L). Conversion from μkat/L to U/L: 1 μkatal/L = 60 U/L

CK-MB concentration /38/: < 10 µg/L (depending on the manufacturer)

Table 1.8-3 Half-lives and time of maximum activity in hours (h) after myocardial infarction /4/

CK
isoenzyme

Half-life
(h)

Peak values
without lysis (h)

After successful
lysis (h)

CK-MM

18*

21

13

CK-MB

12

20

11

CK-BB

3

* 48 h in case of muscle ache

Table 1.8-4 CK and CK-MB activities in acute myocardial injury

Assessment

Angina pectoris

No elevated CK-MB is observed in stable angina pectoris, whereas unstable angina pectoris may cause mildly elevated levels /20/.

Myocardial infarction

The CK rises in proportion to damage; the CK-MB exceeds the upper reference limit after 4–6 hours. In addition, CK activities of over 7500 U/L are indicative of skeletal muscle trauma (e.g., after reanimation).

Myocarditis

Elevated CK and CK-MB is measured in myocarditis; the pattern of the CK-MB can be similar to that in myocardial infarction /6/. Endocarditis and pericarditis only occasionally cause elevated CK levels.

Heart surgery

In an uncomplicated course, cardiac catheter or coronary angiography do not result in diagnostic elevation of the CK-MB /19/. Reanimation, defibrillation and thoracic trauma result in elevated CK activities corresponding to the extent of skeletal muscle trauma; myocardial involvement will also cause elevated CK-MB. Myocardial surgery causes the release of CK-MB; CK-MB levels 2-fold in excess of the upper reference limit 20 hours after bypass surgery are indicative of an infarction /21/. Depending on the severity of surgery, valve replacement and transplantation cause elevated CK and CK-MB with peaks reached after 24 hours in most cases. Stress tests (stress ECG) do not result in pathological elevations of CK and CK-MB /6/.

Miscellaneous

As a rule, no significant increase in CK and CK-MB is observed in tachycardia, heart failure and cardiac valvular defect /19/.

Table 1.8-5 CK and CK-MB activities in acute skeletal muscle damage

Clinical and laboratory findings

Physical activity

Labor/exercise: CK activity increases after major physical labor depending on duration, kind of activity and fitness state of the individual /22/. There exists no limit that allows the differentiation between normal reaction and pathological muscle damage. Especially high activities have been observed after eccentric exercise (e.g., downhill running /23/ and in rhabdomyolysis). After three hours of jogging, the CK-MB concentration increases from 1.5 µg/L to 2.6 µg/L on average within 6 hours /24/. This can simulate AMI unless troponine is determined at the same time.

Diseases: disorders with increased motoric activity, such as tetany, spasms, Parkinson’s disease, fits of coughing, asthmatic state, psychoses or delirium tremens, lead to increased CK activities.

Intramuscular injection

The CK is elevated as a function of substance, volume, concentration and osmolality of the injected solution, and diagnosis of an AMI becomes more difficult /19/. The following substances are believed to cause muscle damage: chlorpromazine, diazepam, lidocaine, pentazocine, pethidine, phenobarbital, procainamide, promethazine.

Surgical intervention

Surgical interventions, traumas, burns, electric accidents, arterial embolisms and pressure necroses that directly affect or secondarily involve the muscles can cause CK elevations in proportion to severity. An elevated CK-MB in thoracic injury indicates involvement of the myocardium /19/.

Acute myositis

Myositides have various causes: Polymyositis, viral myositis (Coxsackie B virus, Influenza A virus), bacterial (leptospirosis) and parasitic myositides (coccidiosis, echinococcosis, toxoplasmosis, trichinosis, cysticercosis). The CK level can be higher than 20,000 U/L.

Rhabdomyolysis

In many cases, CK activities > 5000 U/L are caused by trauma, immobilization, sepsis and vascular and cardiac surgery. The CK is not an important assessment criterion for acute renal insufficiency requiring hemodialysis/hemofiltration and for mortality. A score including age as well as creatinine, phosphate, calcium, bicarbonate and CK is important /25/.

Statins /26/

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors and their therapeutic effect is twofold: they reduce the cholesterol in the low-density lipoproteins and lower the risk of infarction by approximately 25%. The prevalence of statin myopathy is 1.5–5%. Myopathies occur one month to one year on average after the start of statin treatment. Heavy muscle activity is one of the triggers. Moreover, the incidence of myopathies is higher in patients with complex combinations of diseases and patients with a broad range of medication. Other essential risk factors include the statin compound, dosage and drug interactions. In the latter, protease inhibitors (cyclosporin, amiodarone, fibrates) that – like simvastatin, lovastatin and atorvastatin – are also metabolized by cytochrome P450 3A4 (CYP3A4) play a significant role. This results in an increased statin concentration with a toxic effect on the muscles. Cyclosporin inhibits the CYP3A4 and transport proteins, thereby causing a 2–25-fold increase in statin concentration and leading to rhabdomyolyses. Gemfibrozil used for dyslipidemia treatment causes a twofold increase in the concentration of some statins. In combination with simvastatin, amiodarone increases the risk of myopathy by a factor of 10. Myalgias have most often (5–7%) been reported as side effects of statins, but prevalence is only slightly higher than in placebo administration. Myopathies with more than 10-fold elevated CK have been reported in older women treated with cerivastatin. The autoimmune necrotizing myopathy is associated with 3-hydroxy-3-mehylglutaryl1-coenzyme A reductase HMGCR autoantibodies and develops a progressive muscle disease despite discontinuation of statins (see Tab. 25.6-2 – Statin associated).

Laboratory findings: the determination of a basic CK level before statin treatment is not recommended in the guidelines but nevertheless useful. Patients with myopathies often have CK levels that are 3–10-fold higher than the upper reference limit. In such cases, it is not recommended to terminate treatment as long as the clinical symptoms are tolerable. If CK is elevated 10-fold or even exceed 10,000 U/L, it is recommended to terminate treatment immediately. The monitoring of patients with elevated CK includes the weekly determination of the CK activity; depending on the course, the statin will be changed and/or treatment will be continued or terminated. The determination of TSH for excluding hypothyreosis-induced myopathy is important. HMGCR autoantibody should be determined in patients with CK activities of several thousand units during statin therapy.

Pharmacological dosage: dynamic changes in CK have not been observed. Antiarrhythmic agents, β blockers, clofibrate, lithium, phenothiazine and some steroids in pharmacological doses as well as suxamethoniumchloride, halothane, hypokalemic agents and alcohol elevate the CK, whereas prednisone and related steroids and chemotherapy regimes can lower it. In rare cases, malignant hyperthermia or rhabdomyolysis occur in predisposed patients /27/.

Intoxication: common causes of intoxication include amphetamines, barbiturates, ethanol, heroin, theophylline, organic solvents, carbon monoxide. Very high CK activities can be reached if the toxic effect is enhanced by pressure on the muscle. Rhabdomyolysis with extremely high CK (much higher than 20,000 U/L) or malignant hyperthermia can occur in extreme cases. Screening for the detection of predisposed patients are not successful /27/.

Olanzapine: atypical antipsychotic for the treatment of schizophrenia. Acute rhabdomyolysis with very high CK levels can already occur after a few days of treatment /28/.

Table 1.8-6 CK activity in chronic skeletal muscle damage

Clinical and laboratory findings

Chronic skeletal muscle damage – Generalized

The CK is elevated depending on the disease activity; the CK-MB portion can be over 10% in severe cases due to the modified isoenzyme synthesis of the chronically affected muscle. Hence, an elevated CK-MB portion is no evidence of myocardial involvement. Activity levels rarely change within a few hours.

– Muscular dystrophy

In X-linked recessive muscular dystrophy, the types Duchenne (incidence: 1/3,500), Becker-Kiener (incidence: 1/18,000) and Emery Dreifuss (very rare) are distinguished. The incidences refer to the number of male births. Duchenne muscular dystrophy (DMD) is 30% based on spontaneous mutations in the Dystrophin (DMD) gene. DMD results from the absence of dystrophin, which is an essential transmembrane muscle protein in the dystrophin/glycoprotein complex. Clinical symptoms begin to show from the 5th year of age and are progressive, implying that a loss of ambulatory ability will occur at age 10–12 years. CK is a sensitive biomarker. It is 50–200-fold elevated at the time of clinical symptoms and declines with increasing duration of the disease. Diagnosis is obtained by molecular genetic analysis of the Dystrophin gene. An elevated CK-MB portion is no evidence of myocardial involvement.

The Becker-Kiener type is the pelvic girdle form of X-linked recessive muscular dystrophy; it manifests itself at age 5–25 years and progresses slowly. Disability of walking occurs at age 30–50 years. The CK course is the same as with DMD.

Autosomal dominant types (facioscapulohumeral type) and autosomal recessive types (limb-girdle type; distal juvenile type) show CK activities within the reference intervals in some cases and rarely increase to over 2000 U/L.

– Primary myopathies

These include, for example, congenital myotony, glycogenosis type V (McArdle disease), myasthenia gravis and neurogenic muscular atrophies (Kugelberg-Welander disease, Aran-Duchenne disease). Depending on the stage of the disease, these myopathies show CK activities that are within the reference interval or only slightly elevated. The Werdnig-Hoffmann disease shows no CK elevations. In McArdle disease, no 3–5-fold increase in lactate concentration in the blood occurs because of the lack of muscle glycogen phosphorylase at muscular exercise under ischemic conditions. This is utilized for diagnostics in the lactate ischemia assay /29/. Autoantibodies against acetylcholine receptors are typical of myasthenia gravis.

– Chronic myositides

Polymyositis, dermatomyositis, ocular myositis. These myositides show significantly lower CK activities than the acute forms; activities within the CK reference interval are also possible.

Elevated CK can be observed secondarily in endocrinological diseases (hyperthyreosis, hypokalemia, hypothyreosis, pheochromocytoma), intoxication, convulsion disorders, paralyses, lupus erythematosus, multiple sclerosis or sarcoidosis. The CK activity returns to levels within the reference interval upon improvement of the underlying disease.

Table 1.8-7 CK activity in other tissue damage

Clinical and laboratory findings

Pregnancy

CK remains within the reference interval during uncomplicated pregnancy. CK elevations to 2–5-fold the upper reference limit occur as a function of the intensity of labor and duration of delivery; similar activities are observed after Caesarean. This involves CK-MM from the muscles and CK-BB from the uterus and placenta /19/.

Acute abdomen

In prolonged, destructive processes such as necrotizing pancreatitis, acute hepatocellular necrosis, ulcerative colon carcinoma and, especially, mesenteric infarction, CK-BB and macro CK type 2 can cause elevated CK levels /1923/.

Severe disease, malignant tumor

In very severe diseases and malignant tumors (lung, colon, breast, gastric, renal cell, pancreas, prostate, rectal, thyroid, testicular carcinomas), the macro CK type 2 may occur in the serum (in some cases in conjunction with CK-BB) and reflect the course of the disease /30/. The CK level may also be elevated as a result.

Hematological disease

The myeloproliferative syndrome can cause excess formation of CK-BB in leukocytes, erythrocytes and thrombocytes that then enters the blood where it leads to persistent CK-BB activities /31/.

Neurological disorder

Acute and chronic disorders of the CK-BB and CK-mito rich CNS can result in elevation of these isoenzymes in the cerebrospinal fluid. CK-BB can only be shown briefly in the blood if the blood-brain barrier is damaged (neurosurgical interventions, subarachnoidal hemorrhage, traumatic brain injury) /32/. This also applies to apoplectic insult. In most cases, the elevation of CK in the serum often observed in these disorders is due to CK-MM /33/.

Tissue damage

In other tissue damage, elevated CK can be caused by the isoenzyme CK-BB, its postsynthetically modified form macro CK type 1 or mitochondrial CK (macro CK type 2) /6/. CK levels rarely change within a few hours.

Table 1.8-8 Tissue distribution of CK isoenzymes

Tissue

U/g

CK-MM

CK-MB

CK-BB

CKmito

Skeletal muscle

800–4000

4+

(+)

(+)

+

Myocardium

240–800

3+

2+

(+)

++

Brain

up to 550

3+

++

Bladder

up to 135

4+

+

Blood

up to 0.2

4+

(+)

Colon

up to 200

(+)

(+)

4+

+

Umbilical cord blood

up to 1.0

4+

(+)

+

?

Prostate

up to 135

4+

?

Uterus

up to 400

4+

+

Venous wall

up to 60

4+

?

4+, > 75%; 3+, 50–75%; 2+, 25–50%; +, 5–25%; (+): < 5%

Table 1.9-1 Principle of GGT determination

L-γ-glutamyl-3-carboxy-4-nitroanilide + Glycylglycine GGT L-γ-glutamyl-glycylglycine + 5-amino-2-nitrobenzoate

Table 1.9-2 Reference intervals for GGT

Adults /3/

< 40 (0.65)

< 60 (1.00)

Children /4/

1–7 days

18–148 (0.30–